refactor window-list

[NamorNiradnug]

Probably fixes #150

This patch refactors the calculation of WayfireToplevel's width. Instead of recalculating the width manually, it simply does label.set_ellipsize and label.set_max_width_chars.

Also there are a few minor style-ish changes suggested by clang-tidy.

[NamorNiradnug]

Known problem: the WayfireToplevel widget becomes too small when all the toplevels have a short titles.

[NamorNiradnug]

This commit simplifies things but it doesn't fix the problem. Once there are too many windows, the box starts growing, and moving to the right any widgets that are to the right of it.

For example, to the right of the window list, I have volume, network, battery, tray, and clock widgets, and if I open too many windows, the window list starts growing and pushing those widgets off the screen.

Hi Yeah, I know there's the problem, but that's why the PR is still a draft) Thanks for your review anyway!