dispose manually: fixes some exceptions during close
ported content assist to Scala
auto-activate and auto-insert content assistance
improved content assist suggestions

Now suggesting lookahead abbreviations, as well as more relaxed matching for words (single letter/symbol is enough). Autostart completion suggestions on `\` or abbreviation start symbols.
use iterator instead of reversing the whole string
auto-edit strategy to automatically decode Isabelle symbols

Decodes Isabelle symbols, e.g. `\<forall>` when whitespace character is entered after it, or when such symbols are pasted into text.
Merge branch 'content-assist'