Smart Contracts: use decimals right after tokenization

[bchamagne]

Description

The problem identified is tested by "floats are precise" unit test.
We fixed it by transforming all floats into %Decimals{}. Most of the code changed is to allow for decimals in the stdlib.

• write unit tests on lib functions that may return floats (Chain.get_balance etc)

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Unit tested

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[bchamagne]

Closing due to the impact in performance and the fact that it does not fix the problem 100% because we still have an API in json.