Helper functions for UI testing

Added a few helper functions that are required to enter input in the text area in activities while writing UI tests.
Some functions are used to implement mouse drag while UI testing. These helper functions have been used in testing of tests for Read and the link for that is https://git.sugarlabs.org/~gauravp/read/gp94-read/commit/b8e0b39cf83e91038861042a30d1a3b8bb547283.