Update Gradle and other project specific stuff
First update to rewrite.

The library isn't supposed to use Activities anymore. Everything doesn't work yet.
Fix typo sending "this" instead of "mActivity"
Add a few comment to be able to check everything out tomorrow in the morning
Update In app payment util library
Update project properties
Update gradle wrapper
Creation of a handleResult function which handle the result to a purchase workflow. It needs to be called from an onActivityResult.
fixes and correct typos
target new sdk
Add javadoc + a few fixes
remove abstract from PremiumManager class
Change the way to check if a given resource exists, or if the user want to use default
Change the way to check if a given resource exists, or if the user want to use default for UpdateButton
Give a String instead of a res for the Premium Menu button
add static method to get premium from pref to be able to use it from widget
Update the way we deal with user's settings. From HabitRPG's test
Update the way to deal with the Menu Button + clean up the code
Add a Readme
Update readme (quoting the license)