TEIIDDES-2120: Stop relocating xsd files

* FileUtil
* mime.types
 * Function for guessing the file type of a file

* VdbMigrateXsdFilesMarkerResolution
 * No need to migrate xsd files anymore. Just need to open the vdb and
   resave it in order to fix a vdb

* VdbEditor
 * Adds a tab panel for displaying schema files since they are now
   separate from both the models and other files

* Vdb
 * Splits the entries into 3 sets, file, udf jar and schema
 * Automatically detect whether xsds are contained in the model entries of
   the vdb manifest or entries and deal with them separately.
 * This essentially fixes a vdb if it is the 'old' type
 * No longer need migrate method since the xsd files are not actually
   being relocated.

* VdbEntry
 * If the file has no contents and a null stream is produced then return
   -1 for the checksum rather than allowing a NPE

* VdbIndexedEntry
 * Abstract parent class for both VdbModelEntry and VdbSchemaEntry that
   is concerned with managing the indexes of these types of entry

* VdbSchemaEntry
 * Own class explicitly for schemas delineating from both model and file
   entries.

Conflicts:
	plugins/org.teiid.designer.vdb.ui/src/org/teiid/designer/vdb/ui/editor/VdbEditor.java
	plugins/org.teiid.designer.vdb/src/org/teiid/designer/vdb/Vdb.java
TEIIDDES-2120: Fix and add VDB unit tests

* Vdb
 * Utilise VdbConstants
 * Ensures that the full path of the vdb's file does not duplicate the
   path of the tmp folder when saving occurs

* MockFileBuilder
 * 1-stop class for mocking a path, its related IFile and underpinned by a
   real file

* VdbFileEntryTest
* VdbTest
 * Fixes tests to cope with more calls to the mocked paths
 * New tests for exploring the functionality of the vdb
TEIIDDES-2120: Erroneous relativising of path value

* Seems making the path relative to the tmp folder is not a good idea
  since it adds a ../ to its beginning. This causes the createTempFile
  method to fail.

* Causes preview vdbs creation to fail with a "no such file or directory"
  error

* Originally added to stop path being a full duplication of tmpFolder,
  which occurred in some unit tests. However, this does not seem to be
  repeated so removing.
Merge pull request #376 from phantomjinx/8.3.x

8.3.x