Add ability to search for records in translation memory

[ArchiDevil]

• There is a search field in TM viewer like it is done in a glossary view
• There is a button that switches between "exact search" or "similar search" modes
• When it is an "exact search" mode, it searches for a substring that is within an input field
• When it is a "similar search" mode, then it searches for closest 10-20 records with some quite low similarity score (about 20-30%, need to find it with testing)