Shell: separate database conn from bootstrap

This patch moves the database connection parts
from bootstrap in a new class ShellDatabaseConnection,
this means that we have three parts of the Shell bootstrap:

- Shell: container, calls the others, does login & run apps
- DatabaseConnection: sets up database
- Bootstrap: deps, libraries, version policy, splash, icons etc

Change-Id: I259c46b1de5de4dfc36eb30587b155e413f152a6
Merge "Shell: separate database conn from bootstrap"