Add search form

[snytkine]

Add search form and use full text title search from MySQL but if MySQL not available we must show some message or not add search form at all. No reason to also search in Question tags

In the future we will have full text search engine probably lucene and then can index full questions, titles and answers as well as update the search datastore when Question status changes and when count of answers is changes as well as update last-update timestamp.
This will be done via custom event listener and using register_shutdown_function

[snytkine]

Done!