Brewfile: install `moreutils`, if only for `sponge`

Hat tip: @chastell / http://talks.chastell.net/kodio-2014/#/21
Brewfile: install `pv` (pipe viewer)

Hat tip: @chastell / http://talks.chastell.net/kodio-2014/#/39
.osx: Make Dock more transparent

Closes #346.
Brewfile: explicitly list non-default taps