Daily Active User (DAU) Integration

[jhreis]

Convert existing DAU code. We want to anonymously track DAU stats for Brave. This gives us information about number of new installs, and general growth over time. With this information we can calculate other information like Monthly Active Users.

• Move DAU file
• Update preference locations for saved data [maybe] (see New Settings & Typed Preferences #61 (comment))
• Setup DAU timer (what represents an "active" user, currently for iOS this should be 10 seconds, I think currently it is 1
• Port updateDauStatWrapper() from AppDelegate
• Unit Tests

Please note, this does not include integrating the URP lines, as that may not be done yet.

Related:
#63