css: match Bootstrap 3 styles

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
js: fixes and code improvements

* Fixes styles to match Bootstrap 3 styles.

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
js: bugfixes

* Allows to capture more than one screenshot.

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>