New features

[eduardomozart]

Add optional modal to select which template to use when exporting a PDF file.
Add custom fonts support - please read tpl/default/README.txt for more information.
Add "_last" prefix for header and footer files to customize the header and footer of last page.
Add custom CSS selector for last PDF page.
Add @OLDREVISIONS@ selector to show page changelog. It's based on #295 and has the intention to fullfil Klap-in expectations about this feature.
Replace "strftime" deprecated PHP function by "date_format".

A template which uses the new features implemented by this PR are available at: https://github.com/eduardomozart/ScriptUtil/tree/master/Scripts/DokuWiki/dw2pdf

[Klap-in]

I have to find time to review. However, house renovation and two young kids makes this difficult to schedule.

[eduardomozart]

No problem =) Please let me know if you have any questions about this PR.

[Klap-in]

A lot of changes in one pull request. Please split them to make it easier to review. For bigger changes an separate pull requests are preferred. Further split the changes in meaningful commits, not every editor will let you do this, but most IDE can. Then the changes can be studied per commit in a review.

#529 performed a large refactoring of the code, this affects also the files you edited. Please could you apply your changes on the new code?

• The template modal is a variation on Added option to active multiple templates #371?
• The custom CSS selector for the last page is only defined if a back.html page is available in the template?
• old revisions looks a bit complicated at first sight, but might work.
• nice way of implementing fonts in the template. If multiple templates are used, could this result in a lot of duplicates? should we think about that?