Added inital implementation for PSResource class.

1. Added tests for PSSaltr class (30%).
2. Reimplemented some functionality in PSSaltr class.
Added initial implementation for PSResource class.

1. Added Helper class for formatString function
2. Added unit tests for PSSaltr class (30%).
3. Made datatype corrections in several classes.
Merge branch 'master' of https://github.com/plexonic/saltr-ios-sdk