Percentage of units that exceed the max lines rule.

[Sebastiaan127001]

To comply to SIG 4-stars benchmark of unit size, as described here, it would be great if Quality-time could measure the percentage of units that exceed 15 lines (numerator) compared to the complete codebase (denominator).

The rules are:
■ The percentage of lines of code residing in units with more than 15 lines of code should not exceed 44.5%.
■ percentage in units with more than 30 lines of code should not exceed 20.3%.
■ The percentage in units with more than 60 lines should not exceed 6.7%.

for inspiration during refinement of this FR, look into : https://github.com/ICTU/quality-time/issues?q=is%3Aissue+is%3Aopen+percentage

[fniessink]

Investigate whether the SonarQube API can return length of units, per unit.