checkbox-touch: fix test-plan selection lingering

This patch makes cache flush when test plan is selected. This fixes the problem
where potential categories and jobs from previously selected test-plan were
listed after test-plan has been changed.

Fixes: https://bugs.launchpad.net/checkbox-touch/+bug/1399609
Signed-off-by: Maciej Kisielewski <maciej.kisielewski@canonical.com>
checkbox-touch: cosmetic changes to resume session page

This patch makes label on resume-session-screen center aligned, and the font
x-large.

Signed-off-by: Maciej Kisielewski <maciej.kisielewski@canonical.com>
checkbox-touch: make resume session screen display info

This patch makes resume session screen display prompt.

Fixes: https://bugs.launchpad.net/checkbox-touch/+bug/1399626
Signed-off-by: Maciej Kisielewski <maciej.kisielewski@canonical.com>
"automatic merge of lp:~kissiel/checkbox/fix-1399626/ by tarmac [r=zkrynicki][bug=1399626][author=kissiel]"
"automatic merge of lp:~kissiel/checkbox/fix-1399609/ by tarmac [r=zkrynicki][bug=1399609][author=kissiel]"