General webui styling polish and fixes

[kschiffer]

Summary

Closes #921

Changes

• Add a subtle gradient to the header component (according to screen design)
• Decrease logo size (to match screen design)
• Fine tune spacing in the navbar (to match screen design)
• Fix icon color sometimes being 100% black
• Fix styling of the sidebar (to match screen design)
• Fix container width of the grid system (to be more considerate of the console layout)
• Fix layout of radio-button/checkbox group items, to allow proper line-wrapping of items in smaller layouts
• Fix / prevent overflow of breadcrumbs (by collapsing crumbs in smaller screens)
• Remove profile picture placeholder in the header for the time being
• Add a general bottom padding to the app container, to prevent content touching the footer
• Streamline table layout for entities (text, title usage, column layout)
• Improve empty table message (better (generalized) text, more subtle appearance)
• Fix scrolling behavior of the console layout (footer should be fixed at the viewport bottom, content should scroll inside the content section only)
• Various tiny fixes to bring the layout closer to the screen design

Notes for Reviewers

This is lot's of individual small fixes. Might be best to go through commit by commit, instead of via the whole diff.