set current chapter title and badge

Reorganize code in app module addBehaviour function.
Module set-up is separated from tab instantiation.

Chapter module now initialized currentChapter with 0 instead of -1.

Progressbar module keeps references to chapter module as well as chapter
badge and chapter title elements.
Its update function then will update both elements with the current
chapter data.
Its constructor expects only the timeline as the params object was not
needed.

related: https://trello.com/c/MqPNx3ms/87-progressbar-kapitel-anzeigen
fix tab layout by resetting base font size

Flex box rules…. in a way.
minor cleanup in chapter module