Fix for #1001989

This PR adds an ability to plug-in your own semantic highlighters to Scala IDE.

It uses existing extension (one for implicit highlighters) and provides you with some basic 
scaffolding that allows easy plugin creation.

Main classes provided for this are instances of `TraverserDefinition` which provides a way to search 
for certain pieces of code:
 * `AllMethodsTraverserDefiniton` - searches for all method calls on given type (and it's subtypes)
 * `MethodTraverserDefinition` - searches for all method calls of given method
 * `AnnotationTrverserDefinition` - searches for all usages of methods annotated with given annotation
 
(all above by 'method' understands `val`s, `var`s, `def`s and/or `lazy val`s)

Those are then used to create `CustomSemanticAction`, `SemanticHighlightingReconciliation, 
and `SemanticHighlightingReconciliationParticipant` (last one is plugged into Scala IDE).

---

For example to highlight all method usages on Scala mutable collections one has to create 
a plugin with 2 classes inside, one that define traverser and highlihter:

```scala
package

object MutableCollectionHighlighter {
  
  /** Id of annotation, used in plugin.xml */
  lazy val ID = "annotations.demo.mutable"

  /** Traverser that looks for all method calls on children of collection.mutable.Traversable */
  lazy val traverser = AllMethodsTraverserDefinition(
    id = TraverserId(ID),
    message = "Method call on a mutable collection.",
    typeDefinition = TypeDefinition("scala" :: "collection" :: "mutable" :: Nil, "Traversable"))

  /** Preference page */
  lazy val properties = MutableCollectionPreferencePage.properties
  
  /** Highlighting actions */
  lazy val actions: List[JavaSourceViewer => SemanticAction] =
    List(viewer => new CustomSemanticAction(viewer, traverser, properties))
}

/**
 * Custom highlihter for mutable collection methods.
 * 
 * It's plugged to Scala IDE extension (see plugin.xml).
 */
class MutableCollectionHighlighter extends SemanticHighlightingReconciliationParticipant(
  reconciler = new SemanticHighlightingReconciliation(actions))
```

And second with a preference page:

```scala
/**
 * Prefererence page for mutable collections, plugs into extension.
 */
class MutableCollectionPreferencePage
  extends CustomPreferencePage("Mutable collections", MutableCollectionPreferencePage.properties)

object MutableCollectionPreferencePage {
  val BASE = "scala.tools.eclipse.ui.preferences.mutable."
  val P_ACTIVE = BASE + "enabled"
  val P_BOLD = BASE + "text.bold"
  val P_ITALIC = BASE + "text.italic"

  val properties = Properties(
    active = MutableCollectionPreferencePage.P_ACTIVE,
    bold = MutableCollectionPreferencePage.P_BOLD,
    italic = MutableCollectionPreferencePage.P_ITALIC)
}

/**
 * Initializer for custom highlighter, plugs into extension.
 */
class MutableCollectionPreferenceInitializer
  extends CustomPagePreferenceInitializer(MutableCollectionPreferencePage.properties)
```

And plug them into Scala IDE:

```xml
<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.4"?>
<plugin>
   <extension point="org.eclipse.ui.preferencePages">
      <page
            category="org.scala-ide.sdt.core.preferences"
            class="annotations.demo.preferences.MutableCollectionPreferencePage"
            id="annotations.demo.preferences.MutableCollectionPreferencePage"
            name="Mutable collection preferences">
      </page>
   </extension>
   
   <extension point="org.eclipse.core.runtime.preferences">
      <initializer class="annotations.demo.preferences.MutableCollectionPreferenceInitializer"/>
   </extension>
   
   <extension point="org.eclipse.ui.editors.annotationTypes">
      <type name="annotations.demo.mutable"/>
   </extension>
   
   <extension point="org.eclipse.ui.editors.markerAnnotationSpecification">
     <specification
         annotationType="annotations.demo.mutable"
         colorPreferenceKey="scala.tools.eclipse.ui.preferences.mutable.color"
         colorPreferenceValue="224,25,25"
         contributesToHeader="false"
         includeOnPreferencePage="true"
         icon="icons/mutable.gif"
         label="Mutable collection calls"
         overviewRulerPreferenceKey="scala.tools.eclipse.ui.preferences.mutable.rulers.overview"
         overviewRulerPreferenceValue="false"
         presentationLayer="5"
         symbolicIcon="info"
         textPreferenceKey="scala.tools.eclipse.ui.preferences.mutable.text"
         textPreferenceValue="true"
         textStylePreferenceKey="scala.tools.eclipse.ui.preferences.mutable.textStylePreference"
         textStylePreferenceValue="SQUIGGLES"
         verticalRulerPreferenceKey="scala.tools.eclipse.ui.preferences.mutable.rulers.vertical"
         verticalRulerPreferenceValue="true">
	    </specification>
	</extension>
	
	<extension point="org.scala-ide.sdt.core.reconciliationParticipants">
	    <participant
	          class="annotations.demo.MutableCollectionHighlighter"
	          id="annotations.demo.MutableCollectionHighlighter"
	          name="Mutable collections calls highlighting">
	    </participant>
	</extension>
</plugin>
```

Lastly, the below disclaimer is required by the lawyers:

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