Add string resolution by key

[AdamLonger]

39

33

Updates:

• Updated versions
• Now creates a "${className}Keys" class, which stores the key variables used in the string resolution.
• Strings can now be referenced, using the "resolve" method. Examples can be found below.
• The Helper class a new Map<String, dynamic> called "_resolutions". The associated Strings and interception methods can be found inside it, for each resolution key.
• Updated tests