Add linter to check svg path dimensions (#3107)

* Add linter to check svg path dimensions

Float precision is set at 3 which is the default for svgo in .svgo.yml;
precision can be raised over time.

This adds an ignore file with the current paths of non-conforming icons.

This also changes the name of the icon title linter as well so it reads
more nicely than "custom".

* Update CONTRIBUTING GUIDELINES

Add a note on visual imperfections and viewbox problems due to 
optimizing.

Co-authored-by: Eric Cornelisesn <ericornelissen@gmail.com>
Co-authored-by: Peter Noble <PeterShaggyNoble@users.noreply.github.com>