Bug fixes, SDK level 19

* use SDK level 19
* add action to all preference intents (fixes #92)
* use StrictHostnameVerifier instead of HttpsURLConnection.getDefaultHostnameVerifier() (fixes #88)
* use per-WebDavResource instead of static DavHttpClient to enable different settings for different accounts
version bump to 0.4.2

* imports calendar default time zone on account creation