Move them change handling out of the package

Now MEF composition doesn't happen in Package.Initialize anymore.
At least package load has a higher chance to succeed and MEF composition
error no longer makes the whole extension unusable.

Related to #583.
Remove an unused field
Merge pull request #584 from dungpa/fix-package-load

Move theme change handling out of the package
SourceCodeClassifier marks as Unused redundant open declarations
SourceCodeClassifier checks open declarations in nested modules for redundancy

add tests
add SourceCodeClassifier.getLongIdents function
refactor colorizer tests
continue rewriting Colorizer tests
finish rewrite Colorizer tests
Code classifier correctly detects that a duplicated in parent scope open declaration is redundant
SourceCodeClassifier properly deal with multiple open declarations in the same line
SourceCodeClassifier works properly with AutoOpen modules
SourceCodeClassifier works properly with opened statements for relative nested modules
VSLanguageService.GetAllUsesOfAllSymbolsInFile doen't change ProjectOptions.LoadTime based on opened files last change time due to performance
add SourceCodeClassifier tests
failed attempt to work around FCS inability to supply accurate FSharpSymbolUse.Symbol for property accessors
LanguageService.GetAllUsesOfAllSymbolsInFile works properly with extension properties
remove Pos and Range types
trying to make SourceCodeClassifier work with extension properties
fix compilation