Correct runtime constants for tests

[breathx]

File Location(s)

pallets/**/mock.rs

Proposal

Set real existential deposit (minimum balance) for all mocked runtimes. Real value is 10_000_000_000_000. This will break A LOT of tests: they should be fixed. All of the demos we use should send value in [0]&[ED, +inf), all extrinsics are same, etc.

Extra note: feel free to set proper BlockGasLimit for tests as well.

[breathx]

I guess @thecaralice can pick it up