Feature/19 fix classcast exception

[sappenin]

• Broaden the type of Condition used by Fulfillment#verify.
• Add unit tests to validate this change.
• Formatting changes.

Signed-off-by: sappenin sappenin@gmail.com

[codecov-io]

Codecov Report

Merging #21 into master will increase coverage by 0.35%. The diff coverage is 100%.

@@             Coverage Diff              @@
##             master      #21      +/-   ##
============================================
+ Coverage     81.97%   82.32%   +0.35%     
  Complexity      174      174              
============================================
  Files            33       33              
  Lines          1126     1126              
  Branches         99       99              
============================================
+ Hits            923      927       +4     
+ Misses          155      153       -2     
+ Partials         48       46       -2

Impacted Files	Coverage Δ	Complexity Δ
...ple/cryptoconditions/Ed25519Sha256Fulfillment.java	93.75% <ø> (+6.25%)	2 <0> (ø)	:arrow_down:
.../java/com/ripple/cryptoconditions/Fulfillment.java	100% <ø> (ø)	1 <0> (ø)	:arrow_down:
.../ripple/cryptoconditions/RsaSha256Fulfillment.java	93.33% <ø> (+6.66%)	2 <0> (ø)	:arrow_down:
...le/cryptoconditions/PreimageSha256Fulfillment.java	100% <ø> (ø)	1 <0> (ø)	:arrow_down:
...pple/cryptoconditions/PrefixSha256Fulfillment.java	85.71% <ø> (ø)	2 <0> (ø)	:arrow_down:
...e/cryptoconditions/ThresholdSha256Fulfillment.java	94.59% <100%> (ø)	1 <0> (ø)	:arrow_down:

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