use auracle as backend and replace dependency solver

[rmarquis]

The next generation cower backend, auracle, removes several limitation of cower and can be used as a complete backend, as was initially intended. It also provides a very fast topologically sorted dependency solver.

In line with the "great overhaul" (#708), drop the internal solver and use it instead.

• The DepsSolver(), FindDepsAur(), SortDepsAur() can be replaced by just a few lines instead;
• FindDepsAurError() needs to be adjusted
• FindDepsRepo() stays as it is (see replace pactree code by more efficient code #575 for planned improvements)
• The update curl call can be replaced by auracle sync -q
• the whole internal json code can be dropped; the single json call required to get the PkgBases list for handling split packages build should be achieved with formatted auracle buildorder call
• info and search should be adjusted to use auracle info and auracle search instead
• color argument is now enabled by default, relevant code should be adjusted accordingly
• The man page needs to be adjusted