CSS improvements of Angular frontend

[TheJuanAndOnly99]

PR addresses issue https://github.com/finos/traderX/issues/125.

• Added TraderX and FINOS logos to header.
• Made button colors darker.
• Removed "Account text"

Screenshot below of changes:

[maoo]

Thanks @TheJuanAndOnly99 - looks much better now!

@DovOps - I believe we're ready to pass it to marketing, maybe for some low touch social, plus newsletter and "this week at finos"?