It was a dropdown to provide choices of color schemes,
and only one scheme could be shown.
With this commit, multiple color scheme previews can be displayed on
one page at the same time, making admins choose color schemes more
easily.
Theme preview windows are shrinked.
Imported default color schemes.
Co-Authored-By: Misaka 0x4e21 <misaka4e21@gmail.com>
Often we need to amend our schema, it is tempting to use
drop_table, rename_column and drop_column to amned schema
trouble though is that existing code that is running in production
can depend on the existance of previous schema leading to application
breaking until new code base is deployed.
The commit enforces new rules to ensure we can never drop tables or
columns in migrations and instead use Migration::ColumnDropper and
Migration::TableDropper to defer drop the db objects
