new string ViewIdentityActivity_my_identity_fingerprint

introducing a new string key ViewIdentityActivity_my_identity_fingerprint which replaces the previous simple concatenation of "my" (possesive pronoun) and "fingerprint". Facilitates translation into non-English languages where possesive pronouns have to be declined.

* English: "My key's fingerpint"
* German: "Mein Fingerabdruck"

to solve the "Meine Fingerabdruck" issue, and to allow smooth translations into other languages.