[DEPENDENCY] Rails dependency excluded.

The module depends on `activerecord` gem only, no `rails` needed.
The install rake task removed. CLI command `uuids install` added instead.

== Addonds

* Uuids::Generators::Install thor generator.
* `uuids install` task (run `uuids install -h` for help).
* `thor` gem dependency.

== Changes

* `rails` gem dependency.
* `install` rake task.

== Version

New release 1.4.0 launched.