Clear search regex on esc

Clear the regex (filtering) when user presses esc key while typing
in the search entry. The entered text itself does not get cleared.
This mimicks the behaviour of other search bars, such as those in
the browser.

Tuleap: #651
Change-Id: I23b2b45b7227e00b7ed034f1f4e49a274c7e2d8c
1 file changed