Add code to handle ownCloud servers running on IDN

ownCloud instances can run on servers having an internationalized domain
name. This commit adds a conversion function between ASCII and Unicode.
The conversion function is used in the Authenticator and Preferences
activities.

See issue #469.
Merge branch 'idn_hosts' of https://github.com/ogasser/android into idn_hosts

Conflicts:
	src/com/owncloud/android/authentication/AuthenticatorActivity.java
Merge branch 'develop' into idn_hosts
Merge branch 'develop' into idn_hosts
Merge pull request #673 from owncloud/idn_hosts

Suuport for URLs to ownCloud servers running on IDN