Use epub.css as the main default style, with all file formats
except FB2 (which needs fb2.css).
(epub.css has been cleaned recently to be more conforming to HTML
specs and to not include class name based styles - with conditional
compatiblity styles for previously opened documents. It should be
usable on all HTML based documents, except FB2 which has some
incompatible specs.)
Consider all shipped css files other than "epub.css" and "fb2.css"
obsolete, and put them in a sub-menu (these other css files have
not been updated in the same way, and are kept as-is for when a
previously opened document requests one of them).
Add an icon indicating which style is set as default (like it's
been done for the Font and Style tweaks menus).
Also set the font size of the full status bar (available with
cre documents) when the setting "cre_header_status_font_size"
is present in settings.reader.lua (to add manually).
1. It turns out that `device_id` is not defined in unit test environment
which makes the `assert(self.kosync_device_id)` fail and somehow makes `luajit` segmentation fault.
2. In the device spec, stubbing `io.open` will make subsquent `require`
all return boolean value and segmentation fault `luajit`.
This patch is a minimum viable change that makes CI work on both my
local box and Travis.
