Removes migrations in favor of their aggregation.

Removes migrations that are included in ChiliProject 2.4.0 and replaces
them by a new, aggregated migrations migration. This migration checks
for all the previous ones and continues w/ either of the following:

 (1) No migrations that this migration aggregates have already been
     applied. In this case, run the aggregated migration.

 (2) All migrations that this migration aggregates have already
     been applied. In this case, remove the information about those
     migrations from the schema_migrations table and we're done.

 (3) Only a part of the migrations that this migration aggregates have
     already been applied. In this case, fail miserably.
Improves seeds.rb to allow consecutive runs.

seeds.rb now can be run multiple times and should not break instances
that already have data in their DBs by using find_or_create_[...].
This also creates the colors in seeds now.
Moves mail options out into seperate constants.
Restores the generation of users and roles.

Previously, migrations have created those roles and users, now that the
migrations are squashed, that generation has moved to db/seeds.rb. This
does not remove other data seeds from the remaining migrations, you
still need to run those! Using Users' admin scope in seeds.
Adds CHANGELOG entry.
Adds proper limits on wiki content fields.

The limits do not apply to postgres, which is why the schema.rb never
included them. MySQL would have produced a different schema.rb.
Subsequent migrations would break when the limit was not established
in MySQL, leading to a much shorter limit. Yes, that is true, no limit
results in a field of shorter size than the maximum size for fields in
MySQL. Hooray for smart defaults!