Frontend: Start implementing a replacements for the workers: Jobs + JobFactories + JobScheduler

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Jobs: Make sure unstoppable jobs are never too long

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Jobs:
- Make sure that jobs don't take too long to stop
- If an added job has a higher priority than the running one, try to stop the running one

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Jobs: fix syntax error

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: disable workers

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
MainWindow: WorkerDocIndexLoader --> JobIndexLoader

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: ActionRebuildIndex --> ActionRefreshIndex

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: WorkerDocExaminer --> JobDocExaminer

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
MainWindow: Fix JobDocExaminer invokation

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Jobs: when a job raise an exception, display the stacktrace of the code that scheduled the job

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Jobs: when an exception is raised, specify the type of the exception

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: WorkerIndexUpdater --> JobIndexUpdater

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: WorkerDocSearcher --> JobDocSearcher

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: WorkerDocThumbnailer --> JobDocThumbnailer

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: WorkerPageThumbnailer --> JobPageThumbnailer

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Jobs: Fix job priority handling

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: WorkerImgBuilder --> JobImgBuilder

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Jobs: Fix uncatch exception

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: remove crappy comments

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: Fix index (re)loading interruption handling

Signed-off-by: Jerome Flesch <jflesch@gmail.com>