The current handling of settings is a very roundabout leftover from the days of
gconf. Simplify and handle the setting more directly. At the same time move
handling of saving the window state to gsettings instead of saving it to a
config file.
The search dialog is replaced with a searchbar similar to the one used in Sublime.
The following features are implicit and therefore removed:
- "incremental search"
- "remove highlights"
- "parse \n characters"
Code style is applied to impacted files (should have been done in a separate commit but it was being discussed during WIP and the new committed code followed neither the new style nor the old).