Process kraken rewards program events

[yabirgb]

This PR addresses two issues:

• Handle .F assets comming from kraken
• Process deposits for the rewards program.

It is missing:

• the unstaking event since we don't have data. I requested @tewshi to unstake a little amount to generate an event and check but it takes 7 days

edit: I've created a ticket to kraken since it is a bit confusing and I'm waiting for a response

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (eecbafd) 80.51% compared to head (999641d) 80.25%.
Report is 6 commits behind head on bugfixes.

Files	Patch %	Lines
rotkehlchen/exchanges/kraken.py	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           bugfixes    #7526      +/-   ##
============================================
- Coverage     80.51%   80.25%   -0.27%     
============================================
  Files          1098     1098              
  Lines        106663   106785     +122     
  Branches      13330    13353      +23     
============================================
- Hits          85881    85697     -184     
- Misses        18703    18992     +289     
- Partials       2079     2096      +17     

Flag	Coverage Δ
backend	80.52% <83.33%> (-0.55%)	⬇️

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