Elide tab titles left so key information at the end of the string doesn't get cut off

Elide tab titles left so key information at the end of the string doesn't get cut off

Summary:
Tab Titles currently elide right. Generally the more useful information is at the right
side of the string--even more so when full paths are being used.

BUG: 406569
FIXED-IN: 19.04.2

Test Plan:
- No change when tab titles don't get elided
- When tabs show the full path and titles are elided, they're now useful: {F6782447}
- When tabs don't show the full path and are elided, they're elided on the other side which seems maybe a tiny bit better, but at least no worse: {F6782448}

Reviewers: #dolphin, #vdg, elvisangelaccio

Reviewed By: #dolphin, elvisangelaccio

Subscribers: ndavis, elvisangelaccio, kneckermcknacksack, filipf, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D20689