SchemaMgration: Initial migration for the package

When we deploy this change, we'll need to fake this
migration.
SchemaMigration: add NoticeType is_visible field

Notice Types that are not visible won't be displayed
in the UI. That means that the end user has no control
over them.
create_notice_type initializes is_visible, too
Give user control over only visible notifications
Merge pull request #1 from transifex/fix-auto-disabling

Fix auto disabling