Make Graph widged more readable for two sources

[DraganMileski]

Hi There,

I think that it will good to be able to see information lengend on the bottom of the graph widget, containing info what is represented by particular color of the line in the graph. Also, the "0" number on the Y-axis is half hidden.

[fdietz]

Good idea!

I'd also like to add an improved presentation of the x-/y-axis labels. For large numbers these should instead improved, too. For example: Kilo/Mega/Giga/Tera instead of 10000000 Bytes.

[fdietz]

This commit fixes the padding/margin of the y-axis, which was half hidden. The axis labels are now trimmed, for example 10000 will be converted to 10K.

[fdietz]

I've started work on showing a legend in a feature branch:
https://github.com/fdietz/team_dashboard/tree/legend_refactoring