Move Cdb classes into includes/libs/cdb/

Change-Id: I2c4fa605acf5e0cf1fdd4821fe6bcdd690b02759
API: Make `usernames` a local variable

Instead of having a single-purpose instance variable, keep the array
local. This also allows reusing `prepareUsername` for other parameters.

Change-Id: Iea7c3c1f24a371a665ebdbeeb3e827262246f1b3
Merge "Move Cdb classes into includes/libs/cdb/"
Merge "API: Make `usernames` a local variable"