Set WFS protocol version in WFSCapabilitiesReader

**Issue** : if the WFS reader reads a capabilities in 1.1.0 or 2.0.0, the protocol of the layers keep 1.0.0 version.
Now, the protocol version is set depending on WFS capabilities version.

Tests added.
The tests will pass only if WFS support is added in openlayers :

Related PR - WFS/WFST 2.0 : https://github.com/openlayers/openlayers/pull/1075
Related PR - Filters Encoding 2.0 : https://github.com/openlayers/openlayers/pull/1069
Related PR - WFS 2.0 capabilities Format : https://github.com/openlayers/openlayers/pull/1058