fix(i18n): Configure the console font

[lslezak]

Problem

• The some non-ASCII characters are not displayed properly, a filled square is displayed instead
• E.g. when selecting the Czech locale and keyboard some Czech characters are not displayed properly when typing.

Solution

• Read the appropriate console font for the selected locale from the langtable data.
• Unfortunately the systemd-firstboot tool does not support configuring the font so we need to write it directly into the /etc/vconsole.conf configuration file.
• Set the eurlatgr console font also in the Live ISO installer.

Testing

• Tested manually, now all Czech characters are displayed properly.

[coveralls]

coverage: 62.433% (+0.02%) from 62.418%
when pulling efe94f0 on configure_console_font
into cce6555 on master.

[imobachgs]

Please, do not rely on is_empty() in this case. Option<T> is a much better alternative.