TUI - overall governance improvements v2

Related: #117 (closed) and #113 (closed) and #114 (closed) and #115 (closed) and #116 (closed)

Overall governance improvements:

• - Move each css to the separate file: !270 (comment 146598)
• - Extract the both part of the proposals and witnesses: #117 (closed)

Improvements in Proposals tab:

• - Remove proposals id's from proposals data: !270 (comment 146519)
• - Fix the display of No proposals when entering the tab: !270 (comment 146600)
• - Add creation of the proposal to the testned_node.py: !270 (comment 146275)