Fix bug in try_pyqt (this is a remaining of my old logic that should have been removed long time ago) #41
Attempt to fix #42:

Implements a thread pool, it works well on linux
Restore missing line
Added a DelayJobRunner:

- the job is run after the specified delay elapsed
- usefull to prevent jobs to be run when the user types too fast
SearchPanel: make use of the DelayJobRunner
Added the search functionnality using the DelayJobRunner.

The search panel still lacks:
- navigation through occurences
- replace occurences
Remove old style classes (#42)