Usability changes and minor bug fixes

[bphenriques]

In an informal way I did some user tests with specific tasks. After receiving the feedback I made some adjustments and fixed some bugs found by them.

• UIDatePicker was not centered on iPad ;
• Adjusted alert messages ;
• Single tap to edit item on the calendar .

I will now try to add a today widget extension showing the next pill date (tomorrow / next week, etc).

[bphenriques]

Moved CircularProgressView and HorizontalGraphBar to a dedicated cocoapods repo