Solver Improvements

• incorporates solve module cleanup #5502
• uses environment history to distinguish between user-requests packages and packages added to environment only as dependencies of user-requested packages
• adds Solver class to solve module, with API-level methods
• supports no-deps, only-deps, update-deps, update-deps-only-deps, update-all, and freeze-installed depedency specifiers
• adds a PrefixDag class with open_url("") method to visualize environments; not currently exposed to users via the CLI, but can be someday
• adds substantial number of unit tests in tests/core/test_solve.py
• adds two extra index.json files to tests directory to help with unit tests

Clean up CLI user interface

commit 6df3749

• cleans up ProgressiveFetchExtract.execute()
• adds new ProgressBar and spinner code to conda.common.io
• uses spinner for several status update messages (e.g. "solving environment", "verifying transaction")
• removes logging configuration conda/console.py
• replaces vendored progressbar with vendored tqdm

Other

• introduces the use of shadow PackageTypes to give solver extra information about environments
• removes much of the envs_manager.py code for private environments, to be replaced using shadow package concept
• organizes conda info into more coherent ordering cbbe81f
• unifies PackageRecord, PackageCacheRecord, and PrefixRecord data models.
• incorporates paths data, including per-path sha256 sums, into conda-meta PrefixRecord; extra hashing can be disabled using skip_safety_checks config param
• more gracefully handles KeyboardInterrupt exceptions
• adds futures as a hard dependency when running conda with python 2.7 interpreter