Brighten link text color in inverted stock theme

Change-Id: I6a110916eb2c53d92f95d1dc03a107a0c1e35257
Revise the options to hide avatars

- Allow to hide avatars on conversation list
- Allow to hide avatars on stock message thread

Change-Id: Ibc597c43ebc125dd5e8323896ffbd2911c64d753