Add constructor to DynamoDBTemplate that takes a preconfigured DynamoDBMapper

[micw]

solves #91

[codecov-io]

Codecov Report

Merging #92 into master will decrease coverage by 0.04%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master      #92      +/-   ##
============================================
- Coverage     40.58%   40.53%   -0.05%     
  Complexity      336      336              
============================================
  Files            64       64              
  Lines          1752     1754       +2     
  Branches        341      341              
============================================
  Hits            711      711              
- Misses          936      938       +2     
  Partials        105      105

Impacted Files	Coverage Δ	Complexity Δ
...in/spring/data/dynamodb/core/DynamoDBTemplate.java	27.65% <0%> (-0.61%)	10 <0> (ø)

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[derjust]

Hope the new constructor helps :)