This is for convenience of being able to use 'stack build --docker'
without needing to specify an image.

Also removed obsolete commented out 'image:' sections.

Also removes unnecessary whitespace changes to Stack.Package

https://dev.azure.com/commercialhaskell/stack/_build/results?buildId=329

Use a hacked version of store which hopefully requires much less memory.

This bumps us to newer versions of some libraries, in particular
conduit, which were previously blocked by commercialhaskell/stack#4125.
Using a custom snapshot should allow this by bypassing that bug.

Note that the previous workaround for commercialhaskell/stack#4125
should no longer be necessary because:

1. Stack 1.9 will not suffer from that bug
2. To my knowledge, custom snapshots never suffered from that bug

Guess we'll find out when Travis takes a crack at this though!

- lts-11.19
- nightly-2018-07-31

This will be a new library for storing package information. This first
bit overhauls the Hackage index update code, and stores information in a
SQLite database instead of the old caches. This turns out to be
significantly faster for `stack update` calls.

Fixes #3586

Note that it would be nicer to just resume the caching from where we'd
last left off, or to parse the revision numbers from the cabal files
themselves. See the discussion in haskell/hackage-server#779 to see why
that isn't possible.

Implements `--color=never` as default on Windows before Windows 10, if emulation would be required to support ANSI colour codes.

Also updates `stack.yaml`, in order to benefit from `ansi-terminal-0.8.0.4`.

`defaultColorWhen`, exported by new module `Stack.DefaultColorWhen`, establshes the default. That module differs, pending on whether the operating system is Windows or non-Windows (see the conditional in `package.yaml`).

`globalOptsFromMonoid` in module `Stack.Options.GlobalParser` is modified so that the default is an argument rather than a given.

A beneficial side-effect of `defaultColorWhen` on Windows is that it enables ANSI on ANSI-capable native terminals. This allows some existing code in module `Main` to be removed.