AEA-720, AEA-735 transition p2plibp2p to cosmos

[DavidMinarsch]

Proposed changes

Replace default ledger in p2p libp2p connections;
Move generic skills and derived skills to soef and p2p;

Fixes

#1453 , #1495

Types of changes

What types of changes does your code introduce to agents-aea?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING doc
• I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have checked that code coverage does not decrease.
• I have checked that the documentation about the aea cli tool works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

[codecov-commenter]

Codecov Report

Merging #1510 into develop will increase coverage by 0.78%.
The diff coverage is 95.28%.

@@             Coverage Diff             @@
##           develop    #1510      +/-   ##
===========================================
+ Coverage    90.74%   91.52%   +0.78%     
===========================================
  Files          258      258              
  Lines        17400    17367      -33     
===========================================
+ Hits         15789    15895     +106     
+ Misses        1611     1472     -139     

Flag	Coverage Δ
#unittests	91.52% <95.28%> (+0.78%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aea/aea.py	100.00% <ø> (+2.04%)	⬆️
aea/aea_builder.py	100.00% <ø> (+13.70%)	⬆️
aea/test_tools/test_cases.py	84.63% <75.00%> (-0.16%)	⬇️
...etchai/connections/p2p_libp2p_client/connection.py	99.24% <88.88%> (-0.76%)	⬇️
...kages/fetchai/connections/p2p_libp2p/connection.py	99.69% <90.90%> (-0.31%)	⬇️
packages/fetchai/connections/soef/connection.py	98.25% <95.74%> (-1.75%)	⬇️
aea/agent_loop.py	100.00% <100.00%> (+2.06%)	⬆️
aea/cli/add_key.py	100.00% <100.00%> (ø)
aea/configurations/base.py	100.00% <100.00%> (ø)
aea/crypto/base.py	100.00% <100.00%> (ø)
... and 21 more

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