feat: make tickers module keep token exponents too

[hallazzang]

Description

Instead of simply keeping denom-ticker mappings, this PR introduces new Asset type which holds the exponent as well. With this change it's possible to calculate dollar values of an asset correctly with assets with different exponents.

Closes: MILK-66

Depends-On: #63

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[RiccardoM]

@hallazzang can you rebase this please? 🙏

[hallazzang]

@hallazzang can you rebase this please? 🙏

Done!

[RiccardoM]

@hallazzang Can you please resolve the conflicts, and remove all the changes related to the rewards module from this branch (you can see the Changed Files tab for a reference). Thanks 🙏

[hallazzang]

remove all the changes related to the rewards module from this branch (you can see the Changed Files tab for a reference)

But these changes to the rewards module have been made because of the changes in this PR. Without updating the rewards module accordingly, build will fail.

[RiccardoM]

But these changes to the rewards module have been made because of the changes in this PR. Without updating the rewards module accordingly, build will fail.

Got it, thanks. Will mark this module as ready to be merged once the rewards module is merged then (will add the dependency into the description).

[RiccardoM]

@hallazzang Could you please rebase/merge main into this one?

[hallazzang]

Closing this PR because I opened a new PR #89. Reopened.