Remove case insensitivity for budget data package import

The specification keys are case sensitive and we should therefore
not be case insensitive but follow the specification strictly.
Simplify permission checks for datasets

Instead of doing "if True then return True" this just returns the
boolean of the if statements.
Allow updates to datasets via budget data package load

This allows a dataset to be updated by loading a budget data
package (instead of aborting).

The permissions mechanism for datasets read,update and delete which
is accessible via openspending.auth is now also callable directly
on the datasets, instead of loading the pylons template context
variable in a background task.
Minor version 0.16.0

* Updates of datasets via budget data package loads now possible
* Budget data package loads follow spec strictly (case-sensitive)
* Continuous testing fixed (use old version of travis-solr)