[Spike] Analyze possibility of move to epam UUI

There is an idea to move miew-app from bootstrap to UUI.
Try to analyze miew-app code and UUI lib from the following view points:
- Difference in design (does UUI implement everything we use? how far their design is from us?)
- Browser and Devices limitations of UUI (we need Miew to work in different browsers and on different devices)
- Other pros and cons
- Draft estimation

Start by reviewing the miew-app code and the UUI library, focusing on the Bootstrap components and design patterns currently used. Compare feature coverage, design differences, browser and device limitations, and other trade-offs; done means a documented feasibility analysis with a draft effort estimate.

Written by the indexing model from the issue text.