Add ability to switch to Dark Mode for TermPortal

Technically, the switching will be between modern-triton theme and modern-material theme.

Dark mode can be achieved by setting the right value to the style-attribute on the html-tag. That value can be got from ExtJS kitchensink examples. However, some amenments are required at least:

1. Set Filters / Clear filters buttons widths should be increased due to material theme is using uppercased button titles 
2. Align the placeholders in filter window
3. Remove shadows from toolbars
4. Adjust toolbars background color, setup button background color instead
5. Hide ellipsis from left panel's processStatus and status columns 
6. Adjust grid selected record background color 
7. Adjust edit/delete icon colors
8. Add spacing between Client and Term collection displayfields, or make {labelAlign: left} for them
9. Adjust rfc5646-background color
10. Make the font size bigger, and the icon sizes smaller 
11. Remove border radius from green buttons, use another background color
12. Use translate5 logo with transparent background