Merge branch 'hotfix/2.0.1' into develop
Merge branch 'hotfix/2.0.2' into develop
Changed callback to expect return value
Do not check if field exists when adding validator

It might be that we're adding a validator for a later added field.
If the field does not exist, the validator is never called but that
does not cause any problems.
Fixed save_callbacks not working at all
Use current request URI for form action to retain GET parameters
Fixed tests
Added fluent interfaces
Implemented possibility to bind a model to the form
Added weight and scale helpers
Changed weight interfaces to support weightable or aggregate
Do not create weight object if value is empty
Weight helper classes should be in Haste namespace
Moved Form class to Haste\Form namespace
Added date handling components
Added input handling components
Added documentation for weight helpers
Include classes in the test, not the bootstrap
Reworked weight class (now based on SI units) and added unit tests
Removed useless variable