Manually init classes list

[RossinesP]

During initialization, SugarOrm parses all the classes in a specified package and finds all SugarRecord classes. This has been problematic in the past because of InstantRun and newest Gradle build tools.

This commit adds a way to manually declare the list of classes we want to convert to tables.
Simply provide a list of Class objects when calling SugarContext.init() or extend SugarApp and its getModelsClassesList() method.
All of this is obviously optional.

Note that no test and no example app has been written for this modification.

[mention-bot]

@RossinesP, thanks for your PR! By analyzing the history of the files in this pull request, we identified @JonatanSalas, @sibelius and @whoshuu to be potential reviewers.

[coveralls]

Coverage decreased (-0.3%) to 74.536% when pulling d55f915 on RossinesP:manual_init into cb45742 on satyan:master.

[gstorer]

Just a heads up. getModelsClassesList() isn't called anywhere. I had to modify SugarApp.onCreate() to use the list accepting version of SugarContext.init() to get this to work with the method over ride. It works fine manually calling the init method though.