Address book import and export (Trac #1444)

[str4d]

Add a nice way to import and export the address book from/to the Bote PC client (I2P plugin).

Migrated from https://trac.i2p2.de/ticket/1444

{
    "status": "new", 
    "changetime": "2015-01-23T23:51:23", 
    "description": "Add a nice way to import and export the address book from/to the Bote PC client (I2P plugin).", 
    "reporter": "dllud", 
    "cc": "", 
    "resolution": "", 
    "_ts": "1422057083611755", 
    "component": "apps/android", 
    "summary": "I2P-Bote Android: Address book import and export", 
    "priority": "minor", 
    "keywords": "I2P-Bote usability", 
    "version": "0.9.17", 
    "parents": "", 
    "time": "2015-01-23T23:51:23", 
    "milestone": "undecided", 
    "owner": "str4d", 
    "type": "enhancement"
}

[str4d]

As of de9c8f9036ac84a3f2962623abbcd1f4416f17f6 the common backend and the Android UI for this has been implemented. Remaining is the web UI.