#288 Background recompilcation and display in integrated viewer

[HotBlack]

An option to have the current document be background compiled and updated in the integrated viewer. Ideally this would be triggered following each burst of typing.
- An option to set the time the editor has been idle before recompliation would be desirable).
- Don't trigger this behaviour when editing files which can not be compiled (e.g. sty, cls, bib files etc)
- Move viewer to current cursor point in editor.
- Don't trigger this behaviour when in a construct which has not been closed.

[Tim Hoffmann]

I'm considering this, but it will take some time, until we've a good solution