Version bump to 0.7.5

* account settings: show whether CardDAV server supports VCard 4.0
* CardDAV GET: ask for VCard 3.0 or VCard 4.0 (preferred) contacts
* CardDAV multiget: ask for VCard 4.0 contacts if the server supports it
* CardDAV PUT: send VCard 4.0 contacts if the server supports it
* import Apache httpclient-android rev. 1652769 correctly (hopefully fixes #491)