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:
  
• 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:
  

Reviewers: Dolphin, VDG, elvisangelaccio

Reviewed By: Dolphin, elvisangelaccio

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

Tags: Dolphin

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