Adding support for appium capability noReset and two new keywords input value and clear text.

Adding keyword input value which uses set_value instead of send_keys.
Adding keyword clear text.
@babarpramod You'd better check platform for set_value for iOS only
[send_keys() uses the keyboard to input the text. set_value() only works on iOS and sets the value without using the keyboard. ](https://groups.google.com/forum/#!topic/appium-discuss/vWlpKrmAjPE)