Reduce unnecessary calls to detect token types via `SingleChainTokensAutodetector.autoDetectTokens(withContracts:)` and `ImportToken.addDefaultTokens()`

Probably a good chance refactor these 2 ways of adding a "default" token into 1.

Also we should change it so that most wallet+contract+server combinations be called only once per app install instead of once at every launch. Note that some contracts are set to only be added when the balance > 0, they should be called repeatedly with every launch