More standard engine config

[ramontayag]

Makes the configuration of the gem a little bit more like the standard way. Main highlight:

Engine migration files are generated with rails g migration .... This allows for future changes to the db to be handled by Rails (detects which migrations are not there), so that the developer won't need to run special rails g plutus:upgrade commands.

Note: Keep tenant column in the dummy app. Until we merge the feature that always turns on tenancy
(#79), we must keep the dummy Rails app's migrations disjoint from what rake plutus:migrations:install actually copies over

[mbulat]

Which version of rails is this targeting? I think this supports 4.2.6 if we change the documentation for the migration command to rake plutus:install:migrations (i'm assuming it's a typo here, since #66 shows the rake command) Is the binstub required for 5.0? I'd like to make sure we target current stable (ie 4.2.6) until 5.0 comes out of RC.

Also, this is a breaking change for anyone seeking to upgrade from something like 0.8 to this version. I'm okay with that since we're not yet at 1.0. Maybe just a quick note in the readme along the lines of an upgrade path like 0.8 -> 0.12.2 -> 0.13 or something

Thanks!!

[ramontayag]

@mbulat sorry - I missed this somehow! The binstub is not required for Rails 5 - that's just for development. When the developer of the gem calls rails (assuming ./bin is in the path - I like to use direnv for this), they will be calling the right rails for the project.

Sure, I'll add the breaking change note.

[coveralls]

Coverage increased (+0.02%) to 94.54% when pulling 56035ad on bloom-solutions:more_standard_engine_config into 00a98af on mbulat:master.

[ramontayag]

@mbulat what do you think of this change?