Refactor commit 25360110 (customizable xtrn program section menu)

Use the text.dat strings that corresponded with the previous behavior
(used by console.uselect()). The defaults include new-lines, so removed
some hard-coded console.crlf() calls that were added. If you have a
custom section_header_fmt, you'll likely need to add a \r\n to it.

Allow the "External Program Section" title string to be customized
(separately from section_header_fmt, e.g. for localization).

Save/use the current section.

Mouse-enable the program section list.