lapack: add BalanceJob type, remove Job and Comp types

[vladimir-ch]

Dgebal and Dgebak are the only remaining functions that use the generic Job type. This PR adds a dedicated BalanceJob type and removes the Job and Comp types. This breaks the netlib/lapack packages, a follow-up PR to do the necessary changes there is ready.

Updates #570
Updates gonum/lapack#163

It is only an update because:

1. There is still the generic Comp type
2. I'm not sure whether we need a dedicated None constant for each type. There are SVDNone and GSVDNone for SVD but no such constants for eigenvalues. It is probably better to add the missing constants so that it is clear which types allow the None option. Opinions?
3. I want to review the names; after a quick look (G)SVD jobs use (G)SVD as a prefix, EV jobs use EV as a suffix, ...

Please take a look.