WIP: [#272] Implement sample FA2 Indigo contract

Description

Implements a sample FA2 contract in Indigo with some tests as described in #272 (moved)

As of now, the implemented contract,

1. Could support multiple token types, (But for now token metadata only hold the metadata of a single token with id 0)

2. Permits owner or operator transfer

3. Owner hooks are optional

Some functionality was stripped from one of the suggested reference contract (stablecoin) and contract size as well as origination size obtained for both, and operation size was compared.

The modified stablecoin contract's origination size and origination size of contract in this PR was approximately 5899 and 4664 bytes respectively.

Related issue(s)

Resolves #272 (moved)

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