Support/improve test coverage: Added tests for PasswordsController

PasswordsController tests have been added to check if error message
is shown when incorrect data are entered into reset password form.
Removed unnecessary matchers

There is no need for aditional matchers to test for success
or redirect of the response because it's already provided.
Added tests for SessionsController

SessionsController tests to make sure errors message are added to flash
for invalid data and redirect is performed after logout.
Added functional test for registration
Added functional test for authentication
Created FormOnPage module

Module provides basic form funcionality like fill and submit.
It can be configured by form function in the including module.
Added functional tests for password reset
Added container option to FormOnPage module

In order to support multiple forms on page, 'container' option has
been added to FormOnPage module. It will force form to operate only
within a container.
Added test for logout

In order to check whether user is logged in, some changes in test structure
had to be done to work with login helper.
Moved page_objects directory to support
Merge branch 'support/improve_test_coverage'