add minimalDist target and upload a launcher-only dist on s3Upload
For minimalDist use mappings directly instead of unzipping maximal dist
Adds .txt as valid file type to enable editing of text files
remove ABI_VERSION_PROPERTY_NAME which is unused.

Going to do this a different way.
Change ActivatorProperties to export USER_CONFIG_FILE rather than USER_HOME
ActivatorProperties: rename getProperty to getPropertyWithOverrides

this is prep for a no-overrides version
don't lookup user.home in two places
add a getPropertyNoOverrides and use it.

This avoids using "props" directly throughout the file.
Throw exceptions rather than return null on missing ActivatorProperties
remove unused SBT_XMX and SBT_PERMSIZE activator properties
Don't double-namespace env vars for activator.foo props

e.g. to override activator.home you would in theory have to do
ACTIVATOR_ACTIVATOR_HOME without this change, not that anyone
was trying to do that anyway.
Fix indentation in project/activator.scala
Split most of RootConfig companion object into a trait

This allows us to mock it in tests instead of using someone's
actual home directory in the tests.
Don't speculatively load RootConfig.userFutureOption

Doing this means that we always try to load from the
"real" location even during tests.
Separate config version from app version and add upgrade-from version

The idea is that we will change the config version infrequently, so it
is "1.0" not "1.0.7" now. We support auto-migrating from ONE earlier
version, which should be enough if we don't change this often.
For now we will use "1.0" and migrate from "1.0.7," and whenever
we break the config file format we can switch to "1.2" or whatever.
add CONTRIBUTING.md
Bumped Play and sbt-atmos versions.
Bump sbt-rc to 1.0-056f4f25fbde18cfcf42b324eaedaca8a8062e31
Merge pull request #145 from typesafehub/wip/1.0.8-cherry-picks

1.0.8 cherry picks