Problem: token mapping state is not exported to genesis

[yihuang]

Closes: #101

• add fields in genesis and init/export genesis logic

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[codecov]

Codecov Report

Merging #113 (0d42f57) into main (3ea70c5) will increase coverage by 4.06%.
The diff coverage is 50.44%.

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
+ Coverage   21.51%   25.57%   +4.06%     
==========================================
  Files          27       34       +7     
  Lines        1729     2299     +570     
==========================================
+ Hits          372      588     +216     
- Misses       1324     1667     +343     
- Partials       33       44      +11     

Impacted Files	Coverage Δ
app/prefix.go	0.00% <0.00%> (ø)
x/cronos/keeper/grpc_query.go	0.00% <0.00%> (ø)
x/cronos/keeper/hooks.go	0.00% <0.00%> (ø)
x/cronos/keeper/msg_server.go	6.45% <0.00%> (ø)
x/cronos/module.go	59.64% <0.00%> (-2.17%)	⬇️
x/cronos/types/codec.go	0.00% <0.00%> (ø)
x/cronos/types/query.pb.gw.go	0.00% <ø> (ø)
x/cronos/types/tracer.go	0.00% <ø> (ø)
app/app.go	4.03% <2.17%> (+0.08%)	⬆️
x/cronos/keeper/keeper.go	62.50% <5.71%> (-31.84%)	⬇️
... and 18 more

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[thomas-nguy]

lgtm