Fix for cellcounter/cellcounter#189

* Adds new css class 'reset_button' allowing assigning of same on click action to multiple different buttons.
* Extracts open_keyboard functionality into a function
* Adds open_keyboard functionality to reset_counters() function
* Adds new buttons for continue and reset count following completion of the first count only
Merge upstream changes
Merge branch 'master' into cellcounter/cellcounter#189
Merge pull request #214 from jvc26/cellcounter/cellcounter#189

Fix for cellcounter/cellcounter#189