Implement secondary title

[kabalin]

This patch adds an option to section settings that allows defining secondary title. Secondary title will be displayed under the title in the section layout. This is useful when one is using weekly format and want to have a custom topic too (and summary is used for summary and needs to be distinguished from title):

[marinaglancy]

hi Ruslan, how is this secondary title different from the section description? It is not editable inline, it does not have any special styles. In the edit section form the "Secondary title" element is under the "Summary" element but when they are displayed, the "Secondary title" is above it.

I know that you can't change the order in this form but it makes this new field confusing for the user and does not have any benefits, at least in the current implementation

[kabalin]

Hello Marina, thanks for your time looking into this. You are right, it does not add value if duplicating summary functionality. The patch has been modified to show secondary title above the main one. This way it also stays visible when section is collapsed (summary element is not visible in this state).