Feature : add PDF export to time report

[yverhenne]

Add the ability to choose the export format of the time report with a drop-down list.
2 possible choices:
-excel
-pdf

[yverhenne]

La modification 'ajout du fichier composer.lock' n'a pas sa place ici. Je ne sais pas pourquoi elle a été embarquée.

[NicoDucou]

Hi @yverhenne
All good with the code, I've just remove the unnecesary modification in gitignore file and adapted the commit message in the squash and merge to keep only one commit message respecting the rules at the end of /documentation/changelog.html

Thank you for the contribution.