idmap: Fix the problems for runtime overlay.

There is no need to make the string blocking when adding the asset
path, as it will be made by the resources.
After adding the overlay path, it also needs to update the string
blocks.
Scan all the sub folders for framework overlay res.

Change-Id: Iaad019111ae364c319e58dce57dbf4647b38d4c3
CRs-Fixed: 763809