added flag to show kernel logo

Fix bug introduced in 9ba2240d

bump version v0.18.6; potential fix for encoding errors on python2, css/js defaults folder for overriding JT on reset

Added Iosevka font

Change layout/notebook.less file format from UTF-8 to ASCII

match rendered subheading styles for markdown

Make it work no matter what encoding system uses

Problem
 - File encoding of notebook.less is UTF-8 and contains U+200B (ZERO
     WIDTH_SPACE) which is not compatible with ASCII
 - If system default encoding is not UTF-8, file read fails on
 stylefx.py line 290

Applied solution
 - used 'iconv -f UTF-8 -t ASCII' command to change file encoding
 - U+200B character removed during conversion

Update requirements.txt

There might have been an downgrade of the stable release of lesscpy. Now it is 0.11.2, lower than the required 0.12.0. Such conflict is stopping people from upgrading and installing the package.

Please refer to #213 for more details.