[IM] Set switch port type to peering when adding to a virtual interface
[IM] Use ifName directly when generting MRTG configurations

The schema original stored ifDescription (as switchport.name) requiring a
per vendor translation function for generating MRTG configurations:

    IXPManager::Utils::switchporttosnmpidentifier($switchport, $vendor);

However, we now also store the ifName directly (which is what MRTG
authors consider "the only sensible way to reference the interfaces of
your switches.

This commit updates the scripts (and sql views) to use ifName directly
including a new utility function to escape characters such as ':',
'@', ' ' and '&' as required by MRTG.
[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