Change naming from Mesa to Aqua

[denciu]

Description

PR changes naming from Mesa to Aqua in filenames, SC code, TS code and README.

Motivation and Context

Resolves #104

How Has This Been Tested?

Went through solhint, eslint and tsc. Code compiles and tests are working correctly.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Follow-up actions to be done:

• update repo name (README.md points to https://github.com/cryptonative-ch/aqua-smartcontracts.git)
• identify other places where naming should be changed

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly. TODO
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.