Update libs - Material calendar to 1.4.0, RN to 0.20

[fxhereng]

1rst commit:
Fix bug of selected dates (currently not working). It is related with the issue #11

This was due to an annotation import changed since RN 0.19 (see more details).

Also updated the material calendar lib to its last version.

2nd commit:
Add new features: minimumDate and maximumDate
I stayed in the same spirit as the other props, they can be set in both way (String and TimeMillis) like this:

<Calendar
          [...]
          maximumDate={[new Date().getTime()]}
          minimumDate={['2016/07/05']}
          [...] />

[fxhereng]

Up please

[chymtt]

@fxhereng sorry I didn't notice this. Gonna review and merge soon. Thanks a lot!