Refactor the prepareDisplayContext callback as a callback method.

Signed-off-by: Norv <a.w.norv@gmail.com>
Refactor previous currentMessage() into currentContext() and reuse it
for Search controller.
Quick-wrap Search controller as a class and set up a similar callback method
for prepareSearchContext_callback().

Signed-off-by: Norv <a.w.norv@gmail.com>
Merge pull request #5 from norv/te_refactoring_display

Refactoring display