[IM] Use ifName directly when generting MRTG configurations

See https://github.com/inex/IXP-Manager/commit/eac33c97789355aa2b093b24b8b7c47d157d51c4
Merge branch 'im-mrtg-polling' of https://github.com/inex/IXP-Manager into lonap

Conflicts:
	tools/perl-lib/IXPManager/lib/IXPManager/Utils.pm
[IM] Remove non-existant graphs from intra-switch graphs category dropdown
[IM] Bring constants in line with perl libs
Merge branch 'lonap' of https://github.com/lonap/IXP-Manager into lonap
Merge branch 'lonap'
[BF] Fix logic
[IM] Small fixes and improvements.