Better job at inserting completions for higher-order methods

This little changes makes life easier when completing methods that take lambdas and
the call is in infix notation.

* use braces instead of parens
* insert a dummy lambda `x => ???` instead of `f`, or whatever the parameter name is

Fixed #1002250.
Revert "Unused member warning doesn't highlight whole definition anymore"

This reverts commit c659afae0c2d27d78b22a18ca1ca3735cb910a4e.

Fixed #1002209
Fallback to word finder when an error is reported at an offset position
Merge pull request #759 from dragos/issue/revert-wrong-presentation-error-positioning

Revert "Unused member warning doesn't highlight whole definition anymore...
Fixes problem build disabled after clean

Following the merge of #767, doing a clean with 'Build Automatically' on, would
not generate any binaries.
The reason was the job scheduled to update the markers after the classpath check (normal after
a clean) was interrupting the build job. The fix is to put both job at the same priority level,
so they don't interrupt each other.
Also fixes the fact that EclipseBuildManager#clean was called twice for each project.
More tests and fix behavior for call-by-name parameters.
Merge pull request #787 from dragos/issue/completion-HOFs

Completion improvements for higher-order-functions
Merge pull request #790 from skyluc/issue/build-after-clean-disabled

Fixes problem build disabled after clean
Addditionnal changes for ScalaImage API

Move the file to the right folder.
Adds the package to the 'Exported-Package' list
Merge pull request #794 from skyluc/issue/API-ScalaImage-2

Addditionnal changes for ScalaImage API
Initial stab at a cleaner interface for Scala presentation compiler.
Remove Scala prefix in ScalaPresentationCompilerProxy
Reformat LocateSymbol
Embellishments and docs on LocateSymbol.
Moved internal classes to internal package.
Remove `doWithSourceFile` from InteractiveCompilationUnit.

A `sourceFile` can easily be obtained from the compilation unit,
and does not justify having an ARM method for (there is no cleanup
or other lifecycle management that needs to be performed around it).
Remove useless `withParseTree`.
Move newSearchableEnvironment to a better place.

The operation made no sense for compilation units, since it
returns a searchable environment for the whole project. Now
it lives in IScalaProject.
Renamed scheduleReconcile to initialReconcile.

After the quiescence changes, this method is no longer doing what it
said it does. To clear up terminology, we reserve `schedule` to mean
scheduling a future askReload (pc.scheduleReload). All units scheduled for
a reload will be passed to `askReload` on reconciliation timeout (usually
500ms).

This method is the entry-point to the managed units in the presentation
compiler: it asks for an initial Reload and adds the unit to the managed set, so from now on `scheduleReload` can be used instead. When dirty units are flushed, all units that are dirty but that are not in the managed set are discarded.
Reviewer’s comments, removing the last uses of `askOption`.