Make all DATETIMEs UTC

This PR means that all times are converted to UTC before they are saved and converted back the local timezone before they are returned to the client

#### PG
Uses columns of type `TIMESTAMP WITH TIME ZONE`. This means that the fact that this is a UTC time is saved in the DB, and when we do new Date, the timezone is automatically converted.

#### sqlite
Uses toSqlDate to create a UTC date, and manually appends a Z (= UTC) to the result before doing new Date

#### mysql
Uses toSqlDate to create a UTC date, and uses the newest version (alpha7) of node-mysql, which allows you to specify a timezone setting when connecting. This is automatically applied by the built in parser of the lib before the result is returned to sequelize.