(Improvement) Use pure/view instead of const on functions

[garatortiz]

Before submitting a pull request, please provide the following information:

• What is it? (leave one option)
  • (Improvement) of existing functionality

Please also put it into pull request title, e.g. (Fix) confirmation page loading

• What was the root cause of the problem originally / what feature was missing? Some functions in smart-contracts were using const.

• How does this pull request solve it (in broad terms)? Replace const with pure/view

• Does it close any open issues? Closes #146

• Quick checklist

  • [x] npm run lint shows no errors
  • [x] docs were updated where necessary OR they don't need to be updated
  • [x] tests were updated where necessary OR they don't need to be updated

• Additional information