ENH: Added graph sort to conda dependency resolution
TEST: added toposort tests
FIX: for python3
ENH: removed obsolete code

@asmeurer
ENH: updated cycle detection to pop sorted key

`pop_key` will pop an item from the graph that has the fewest dependencies
In the case of a tie, the winners will be sorted alphabetically.

cc @mattpap @asmeurer
FIX: python3
update changelog
add --offline option to install, create, update and remove commands
fix case when channels are undefined
fix CONDARC pointing to non-existing file, closes issue #961
update changelog
Merge pull request #1009 from conda/feature/topo-sort

Added graph sort to conda dependency resolution
Add some more help to conda config
Merge branch 'master' of github.com:conda/conda
Fix possible TypeError when printing an error message

See #1021.
Make update -f work if the package is already up-to-date
Merge remote-tracking branch 'conda/master' into feature/env-activation