World map enhancements

[mblue9]

To resolve https://github.com/elixir-europe-training/ELIXIR-TrP-Training-Metrics-Database-Tango/issues/26

• Apply a log transformation to the color scale
• Use a single color gradient instead of a viridis scale

I used ELIXIR orange as it looks better to me than the ELIXIR blue for this, but happy to hear other opinions.

[unode]

Agree that orange and log scale looks great. Thanks for the changes.

[unode]

In my opinion, ready to merge unless someone objects.

[mihai-sysbio]

Just making a note here that this PR also resolves #18.