Checkboxes under TOC>Settings> allow enabling Custom TOC
and Custom hidden flows (similar to "Hide non-linear fragments"
available with some EPUBs).
Handled by a new ReaderHandmade module.
Adding and removing TOC chapters is done in PageBrowser
with long-press on a page thumbnail, and for chapters also
in the popup dialog after selecting some text in a page.
ReaderToc: add a symbol in title when the TOC is the
alternative TOC or the custom TOC.
