Make theme compatible with SASS 3.3.4

From the mailing list:

I wanted to compile a custom theme for my OO 9.3.1 installation, using the provided compile_theme.sh script. I have the latest SASS 3.3.4. Compiling a child theme based on the openolat default theme, this SASS error from the core theme pops up:

error …/openolat/all/_icons.scss (Line 32: You may not @extend an outer selector from within @media.

You may only @extend selectors within the same directive.

From "@extend .b_with_small_icon_right" on line 434 of …/openolat/all/_basemod.scss.

I did a quick&dirty fix by removing the @extend in _basemod.scss and replacing it with the rules for .b_with_small_icon_right from _icons.scss.