Add a removeDifference action

The removeDifference action deals with the 'differences format' as follow:
<differences>
	<difference>difference #1</difference>
	<difference>difference #2</difference>
</differences>

Each difference can be removed thanks to a regex pattern in the object input.

Result is affected to the given Property input. Thus, the Property input can change at every call of the removeDifference action.

For instance:
	- by using the following removeAction with
		- Object = .*foo.*
		- Property =
			<differences>
				<difference>foo</difference>
				<difference>bar</difference>
				<difference>foofoo</difference>
			</differences>
	- then the result will be :
		- Property =
			<differences>
				<difference>bar</difference>
			</differences>

Closes #302