Make operations on the feature selection more memory friendly
Attribute form: do not try to edit non-editable fields
Add better Null support to QgsFilterLineEdit
Better QgsFilterLineEdit support for several edit widgets
Update sip bindings
[FEATURE] Add suffix support for range widget
[FEATURE] SSL PKI integration for OWS connections (sponsored by Boundless Spatial, US)

- Add SSL certificate settings and utilities classes
- Setup local ~/.qgis2/cert_store setup
- Add QgsCredentials key passphrase support, with stacked widget to rotate between inputs (username/password or key passphrase)
- Add SSL Certificate widget to new OWS connections (tabbed widget with Authentication)
- Cache key passphrases in QgsNetworkManager singleton, since it did not work with QgsCredentials
Add SSL PKI support for WMS connections
QgsCredentials PKI key passphrase cache that doesn't seems to work (cache gets lost across threads?)