Context missing in UI

[khatchad]

We should see the function being discussed. Instead, the pane says "no context available:"

[khatchad]

Added a simple function context in acd5740, which only highlights the function name and doesn't provide syntax highlighting. Pending items are:

• Provide the complete function context. Currently, this is difficult, because the end offset is not readily available. There's a possibly to pass over the ASTEntryWithChildren, which has ending lines and columns.
• Syntax highlight the context. Currently, we are using a file context, which provides no syntax highlighting. It would be better to make a context similar to what is done in Java, but this is quite complex.