Changed all Cipher and Signature method variables to object variables
Fixed Javadoc
Changed all non-private CryptoUtils methods to synchronized
CryptoUtils now throws RuntimeExceptions for fatal initialization errors
Refactored exception handling in CryptoUtils.
Exceptions which are the result of invalid input values are now thrown
Changed Mac method variable to object variable
Naming in drop message was wrong
Fixes singular/plural naming inconsistencies in config classes

This changes some names of collection members and collection returning
getters to indicate the plural.

Closes #103
Merge pull request #161 from L-Henke/cryptoUtilsRefactor

CryptoUtils refactorization
Small cosmetic changes
Removed usage of model class Contacts from drop interface

According to the model-view-controller concept, the Contacts class
should not be exposed in the drop interface.
Instead, a collection of "Contact"s is used.
Merge pull request #151 from cburkert/fix_mvc_incompliant_usage_of_contacts

Removed usage of model class Contacts from drop interface.
Update class diagrams
Merge pull request #178 from k-c13/update-diagram

Update class diagrams
Merge pull request #167 from cburkert/fix_naming_inconsistencies

Fixed #103 singular/plural naming inconsistencies in config classes
Merge pull request #163 from k-c13/drop-message-naming

Fixed Qabel/qabel-doc#69 - Drop message fields were named incorrectly in the implementation.