Autocomplete Improvements

[rcosta358]

This PR improves the autocomplete suggestions by:

• Not suggesting ghosts/states from different classes (aliases are fine)
• Implementing annotation-specific suggestions
• Implementing trigger characters (" and .)
• Suggesting ghosts/states after this. or old(this)
• Suggesting parameters in method and parameter level refinements
• Not suggesting return unless we are in a method level refinement (still shows for field refinements)
• Having autocomplete work even in the presence of LiquidJava errors (when an error occurs, subsequent variables are not added to the context and therefore are not suggested)