Support creating a table migration generator

Sometimes you want to create a table without an associated model and
test, which is also not a join table. With this commit, you can now
do that.

Example:

    rails g migration create_posts title:string
or
    rails g migration CreatePosts title:string

This commit also moves the template the model generator uses for the
migration to the migration templates folder, as it seems a more
sensible place for it now that it is shared code.
Merge pull request #8652 from codeodor/create_table_migration

Support creating a table migration generator

Sometimes you want to create a table without an associated model and
test, which is also not a join table. With this commit, you can now
do that.

Example:

    rails g migration create_posts title:string
or
    rails g migration CreatePosts title:string

This commit also moves the template the model generator uses for the
migration to the migration templates folder, as it seems a more
sensible place for it now that it is shared code.
don't use non-ascii ' chars in documentation
Fix PostgreSQL TIMESTAMP WITH TIME ZONE to return ActiveSupport::Time

In an AR model a timestamptz attribute would return a ruby string and AR
tests did not check for any type casting.  Previous tests would pass
only because an assert_equal was being used on a Time.utc object, which
will parse the right side of the eq to a valid Time instance for
comparision.

switch to test instance of Time instead of ActiveSupport::TimeWithZone
New beauty pages(404, 422, 500)

moving changelog note to unreleased section

New beauty pages(404, 422, 500)
Restore note about nested SCRIPT_NAME handling.
deal with `#append` and `#prepend` on association collections.

Closes #7364.

Collection associations behave similar to Arrays. However there is no
way to prepend records. And to append one should use `<<`. Before this
patch `#append` and `#prepend` did not add the record to the loaded
association.

`#append` now behaves like `<<` and `#prepend` is not defined.
Merge pull request #9510 from senny/7364_warn_when_appending_prepending_to_an_association

deal with `#append` and `#prepend` on association collections
:scissors: extra blank line
Merge pull request #9431 from troyk/patch-2

Fix PostgreSQL TIMESTAMP WITH TIME ZONE to return ActiveSupport::Time
Remove hard coded references to Active Record in railties
Merge pull request #9512 from Jacke/master

New 404, 422, 500 pages, they are more stylish and bring ruby essence…
integrate the strong params README into the AC guide.

The current ActionController guide does not mention strong parameters
at all. I integrated the README into the guide to explain the API.

I also included a section to illustrate that the API does not solve
all possible whitelisting scenarios.

The origin was #9454.
Merge pull request #9465 from senny/document_strong_params_in_ac_guide

integrate the strong params README into the AC guide.
Fix ActiveRecord `subclass_from_attrs` when eager_load is false.
It cannot find subclass because all classes are loaded automatically
when it needs.