Fix #940, update() passing boolean to modified_on()

BF_Model's update() method was passing the validation result to the
modified_on method (if validation failed and set_modified was enabled).
Fix #941, Model set_date with GMT time_reference

Use gmdate() instead of date() if CI's time_reference config is set to
GMT.

Note that CI 3 doesn't use time_reference, so this can be reverted
when/if CI is upgraded to v3
For #925, Pull markup out of Contexts methods

Pulled the markup out of the methods in the Contexts class to
(hopefully) make it a little easier to replace the markup according to
the desired framework. Likely still needs some work, since the templates
are still built around the structure of Bootstrap 2.
Changelog updates
Lowercasing the model name so that models can load, even when called with a ucfirst name. Fixes #948
Merge branch 'develop' of github.com:ci-bonfire/Bonfire into develop
Updated changelog
Fixed small bug that would cause an invalid redirect on certain systems when saving the settings.
Merge pull request #950 from tolusonaike/develop

Fixed "delete_where" example in docs
Merge pull request #1 from ci-bonfire/develop

pull latest changes into my fork