Register ISimplelayout and ISimplelayoutBlock marker interfaces as DX behavior.
Make text field of TextBlock searchable.
Implement ISimplelayout container indexer (Index searchabletext of all simplelayout blocks).
Test searchableText of ISimplelayout container on move, copy and delete.
Merge pull request #62 from 4teamwork/mle-searchabletext

Implement indexing the searchableText of blocks on ISimplelayout container.