Migration Driver for SQLite

Need more tests.
Integrate MigrationDriver to migrate.go
Fix migration step not checked against current version.

Add tests for DropColumns.
More tests for alter columns migration

Also change the way we handle columns rename migration.
SQLite restrict column addition not to have PRIMARY KEY and/or
UNIQUE attribute, so we have to change from:

add new column -> migrate data from old column to new column ->
rename old table -> create new table with old columns removed ->
migrate data from old table to the new table -> drop old table

to directly:
rename old table -> create new table with renamed columns ->
migrate data from old table to the new table -> drop old table
Add tests to migrate existing database without migration attributes.
Integrate migrations with drone.

Also add migration to tests.
Added GitHubApiUrl and GitHubDomain to settings and template
Put values from settings into handler/auth.go
Use custom github domain for webhook
Update all github clients in code
Added settings to github_add page (fix redirect)
Fixed identation
Make IsGit check less strict
Fixed another github client instance in code
Migration file based on #83

I choosed Rev3, because Rev2 will be about "open invitations" feature.
Add form tag to make install work.

There seems to be no javascript to post this form and no form tag to make the form work so added one
Merge pull request #87 from pythonandchips/master

Add form tag to make install work.
make smtp-auth optional
Merge pull request #88 from notandy/master

Make smtp authentication optional
fixed template issue with install screen, not using correct base