Implement Search

[teamcons]

fix #39
requires #52

The search is very crashy, though it correctly finds a few words... if you copy paste them.
I am still working on this. But the UI part fully works so you can already get an idea

If you plan a toolbar, i can move the content of the revealer into a neat little popover though

[teamcons]

Okay search fields have been moved from a revealer to a popover
The popover version leaves the space for a toolbar, but i feel like having the search not be a menu but always-there is more comfortable
moving the whole textview to reveal a bar feels overkill

The search now works semi-ok, and there is a smooth scrolling to go to the found term

the big blocker i now have is that TextIter is not supposed to crash if it rewinds/search too far/doesnt find anything. It is supposed to return a False.

[teamcons]

Okay

-At current, the search always starts from the end. I will get around to fix this but havent found yet

-because of TextIter search methods apparently crashing instead of returning a boolean, search relies on a very dirty workaround to ensure search without crash. If someone opens huge text files they will notice (the method scans at worst the whole buffer three times for one term search)

[teamcons]

Okay

@wpkelso Could you please try it out and let me know what you think, if that is ok with you?
(no pressure though :) )

Because of a bug that forces me to do an ugly workaround to avoid a crash, it is not "optimal", but a search through 10 times the whole Martin Luther King speech has no sign of slowing the UI down.