[Swapper] Improve approval check inside fetch_quote

[0xh3rman]

Currently erco20 approval check is done at the end of fetch_quote method, things can be improved like:

1. Call it in parallel to reduce quote time
2. Move it up from provider level to swapper level
3. Move it to fetch quote data

[gemcoder21]

I would recommend adding caching to approval case, once token has an approval for the amount (or max amount) there is no reason to check for in this session (it would be very rare case that a user would revoke approval in current session)

[0xh3rman]

Will be merged into #385