Add a script to create a dist directory for use by apps

The idea is for dist to contain everything a client app needs to build
against libchromiumcontent.
Fix Debug vs. Release builds of libchromiumcontent

The Debug version of chromiumcontent.ninja was overwriting the Release
version (they were both being generated into vendor/chromium/src instead
of vendor/chromium/src/out/{Debug,Release}). So now we copy
chromiumcontent.gyp into the vendor/chromium/src tree so it works like
all other Chromium gyp files.
Copy .dSYM bundles into the distribution
Create distributions in CI
Zip up the distribution
Link the fake dSYM into a real one
Add some logging output
Blow away dist/ each time so we don't end up with old files