Fixed thread related issues.

Added a data member m_bExecute which defaults to true but is set to
false when StopExecution is called. During execution, the member's value
is checked at various positions, if it is false, the execution is stopped
by returning from the execute method.

Following issues have been resolved:

* Multiple searches can be performed. The previous search is halted.
* Cancel button can be pressed in between any search or application of
  the persona.
* A theme can be selected and applied by clicking on OK while the search
  is being done.

Change-Id: Ic76c224ca0d317a6e1a44b3e8933a3ba50b371cb