Add txprovider to ease transaction usage

[codecov-io]

Codecov Report

Merging #24 into v2.3.x will increase coverage by 1.48%. The diff coverage is 100%.

@@             Coverage Diff              @@
##             v2.3.x      #24      +/-   ##
============================================
+ Coverage     45.33%   46.81%   +1.48%     
- Complexity      446      465      +19     
============================================
  Files            47       48       +1     
  Lines          2111     2121      +10     
  Branches        242      242              
============================================
+ Hits            957      993      +36     
+ Misses         1009      981      -28     
- Partials        145      147       +2

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/com/syncleus/ferma/tx/TxFactory.java	100% <100%> (ø)	6 <6> (?)
src/main/java/com/syncleus/ferma/tx/Tx.java	80% <0%> (+80%)	3% <0%> (+3%)	:arrow_up:
...rc/main/java/com/syncleus/ferma/tx/AbstractTx.java	84.61% <0%> (+84.61%)	10% <0%> (+10%)	:arrow_up:

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[Jotschi]

@freemo I updated the PR. It now includes tests for the newly added code. Is there a way to re-run the codecov checks?