Polished LoadData and error messages

Moved error messages handling from LoadData-class to Activity-classes.

LoadData methods now throw exceptions catched by Activity-classes.
Error messages displayed in ErrorView instead of ListViews.

Implemented method in BaseActivity that checks Internet connection.
Merge branch 'develop' of https://github.com/jonasberglund/skrubb_DAT255 into develop

Conflicts:
	H-sektionen/src/se/chalmers/h_sektionen/utils/Constants.java