Add tools for distance, coordinates, terrain profiles

[andrenarchy]

Add simple tools:

• measure distance between 2 points
• get coordinates of a point
• plot terrain profile, see [webui] plot terrain profile libremesh/libremap#2

[elf-pavlik]

some useful leaflet plugins from http://leafletjs.com/plugins.html

• https://github.com/MrMufflon/Leaflet.Elevation
• https://github.com/makinacorpus/Leaflet.MeasureControl
• https://github.com/MrMufflon/Leaflet.Coordinates

[mojoaxel]

I don't see any use for the Elevation plugin but the MeasureControl would be great!

[nicoechaniz]

mojo, the terrain profile is very useful to "calculate" link feasibility. It's of little importance if your network is on flat terrain, but very relevant in hills/mountain regions.

elf, the plugins look neat :)