Add an option to disable Gray out unused declarations
Refactor syntax coloring
Merge pull request #541 from dungpa/unused-symbols-option

Add an option to disable Gray out unused declarations
try to fix the issue with ModuleSuffix attribute
extract AssemblyContentProvider from LanguageService
AssemblyContentProvider works properly with entities included into modules with CompilationRepresentationAttribute (CompilationRepresentationFlags.ModuleSuffix) attribute
fixed: UnopenedNamespacesResolver does not work with anonymous modules properly
add icon to "open namespace" smart tag action