Enable marking message as unread in web interface (Trac #1737)

[str4d]

On I2P-Bote Android we can mark a message as unread. On the Material themed HTTP interface for PC I could find no way to do it.

Migrated from https://trac.i2p2.de/ticket/1737

{
    "status": "new", 
    "changetime": "2015-12-17T12:02:00", 
    "description": "On I2P-Bote Android we can mark a message as unread. On the Material themed HTTP interface for PC I could find no way to do it.", 
    "reporter": "dllud", 
    "cc": "", 
    "resolution": "", 
    "_ts": "1450353720970551", 
    "component": "apps/other", 
    "summary": "I2P-Bote: Cannot mark message as unread on http interface", 
    "priority": "minor", 
    "keywords": "I2P-Bote, usability", 
    "version": "0.9.23", 
    "parents": "", 
    "time": "2015-12-17T12:01:22", 
    "milestone": "undecided", 
    "owner": "str4d", 
    "type": "enhancement"
}

[str4d]

Trac update at 20151217T12:02:00: dllud changed component from "unspecified" to "apps/other"