Feature v4 convergence for linops

Closes #858.

Reverts to the equivalent of Version 4 convergence testing for linops. It's more aggressive than plateauCheck but still passes the tests. 
It's generally best to have an inner solution a little more accurate than an outer iteration is trying to be. However, the code originally checked in was an old attempt to do that through vscale. Instead I'm now using the errTol property. 

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