Make log files more readable

[smarr]

The ReBenchDB log files currently don't have a lot of useful info.

It looks for instance like:

Generate Report: Rscript '/home/node-deploy/sites/ReBenchDB/dist/src/../../src/views/somns.R' 'TruffleSOM-b23165-4d20e8.html' 'TruffleSOM-b23165-4d20e8_files' '/home/node-deploy/sites/ReBenchDB/dist/src/../../src/views/' 'b231656f4decfd6c5d41b442b4bf7a121b920450' '4d20e8976cfe778008a6f1439a193a5626c08014' '#729fcf' '#e9b96e' 'rebenchdb' 'nodedbs' 'rebenchdb-2019' ''
/rebenchdb/results: stored 185 measurements
/rebenchdb/results: stored 10 measurements
/rebenchdb/results: stored 170 measurements
/rebenchdb/results: stored 70 measurements
/rebenchdb/results: stored 110 measurements

Would be good to keep at least time info, but perhaps also other details that makes it easier to read and understand these logs.

[smarr]

This is done as part of #106.
We're now using the tslog library for logging.