Placeholders in description

Replace description placeholders from captured expressions in found indications

Substitutions may be made within the description with
placeholders of the form ${I,G}, where I is the indication
number and G is the captured group within the indication
expression. e.g., ${1,1} would be replaced with the first
indication's first captured group and ${1,2} would be
replaced with the first indication's second captured group.

This work was originally based off of [Novakov:placeholders_in_description (Pull Request #4)](https://github.com/jenkinsci/build-failure-analyzer-plugin/pull/4)
Which access level modifier should it be?