Improve error messages and error handling

[earaujoassis]

It's been tricky to obtain error messages when requesting something from the API or from the view side (mostly, OAuth methods). The error message and handling should be improved on those areas, mainly:

• Creating and updating user data (error messages for each scenario);
• Creating session tokens and their error messages involved; and
• Creating and updating client applications (error messages for each scenario).

[earaujoassis]

Display error/panic messages for development environment through the 500/internal error page.