Add moshi adapter for big decimal numbers; Remove factory

[elgatovital]

Closes #48

Changes proposed in this pull request:

• adapter for big decimal numbers
• remove factory

@gnosis/mobile-devs

[codecov-commenter]

Codecov Report

Merging #49 into master will increase coverage by 0.38%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master      #49      +/-   ##
============================================
+ Coverage     60.17%   60.55%   +0.38%     
  Complexity      154      154              
============================================
  Files            55       55              
  Lines          1401     1397       -4     
  Branches        233      233              
============================================
+ Hits            843      846       +3     
+ Misses          440      433       -7     
  Partials        118      118              

Impacted Files	Coverage Δ	Complexity Δ
...ava/pm/gnosis/common/adapter/moshi/TypeAdapters.kt	94.44% <100.00%> (+30.80%)	0.00 <0.00> (ø)

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