Remove "Close Tab button" option and related functionality

The `browser.tabs.closeButtons` preference has been removed since Firefox 31.
So this functionality became redundant.

Related to ithinc/tabutils#114.
Add warn logging in case when nothing was replaced in `TU_hookFunc`
Remove "Donate" button
make.sh: Fix file mode
Revert "Remove "Close Tab Button Position" functionality"

This reverts commit 4c2b338c677e8eff43482f70e88b32e7683ee05c.
Remove "Close Tab button on tab bar" related options
dev

Add "Close Tab button" functionality

(not working yet)
dev