Api get router by mac or hostname

In addition to 
router-id: `https://netmon.freifunk-franken.de/api/rest/router/518`

this is now also possible:
mac: `https://netmon.freifunk-franken.de/api/rest/router/e894f62983a8`
hostname: `https://netmon.freifunk-franken.de/api/rest/router/DieBar`