Improved Cisco icmp-jitter IP SLA integration

This patch is designed to poll and graph info from the Cisco's CISCO-RTTMON-ICMP-MIB for the IP SLA probe `icmp-jitter`.
These probes were correctly discovered by Observium, but only RTT was polled from them.
With this patch, poller will create 5-ds RRD files for icmp-jitter probes, ds include:

• average rtt (ds name: rtt)
• min rtt (rtt_min)
• max rtt (rtt_max)
• number of sent packets (req_count)
• number of lost packets (loss_count)

Module includes/polling/cisco-sla.inc.php was rewritten to allow creation of these 5-ds RRDs.
Graphing module was re-built to handle these new RRDs - part of this module, building-up the RRD command, was splitted into 2 modules, for regular echo and icmp-jitter respectively.

Currently, there's no mechanism of adding 4 ds (rtt_min, rtt_max, req_count, loss_count) to RRDs for existing icmp-jitter probes (with 1 ds for rtt only), only new RRDs for icmp-jitter can be created and correctly.

This patch also requires new config.php options to look like:
$config['sla']['loss_color'] = array('55FF00', '00FFD5', '00D5FF', '00AAFF', '0080FF', '0055FF', '0000FF', '8000FF', 'D400FF', 'FF00D4', 'FF0080', 'FF0000');
$config['sla']['loss_value'] = array(0, 2, 4, 6, 8, 10, 15, 20, 25, 40, 50, 100);

I've moved MIB file CISCO-RTTMON-ICMP-MIB.my from mibs/cisco to mibs and renamed without extension (to CISCO-RTTMON-ICMP-MIB) to make snmpwalks in this patch.

And also notice: Cisco supports this IP SLA type on IOS routers only. None of the Catalysts, IOS-XE and IOS-XR routers support this..
They have a path-jitter |IP SLA operation, whose statistics are not accessible via SNMP, only via CLI