BrowseFragment: Fix regression from bfe8cc0.

We received a crash report of someone trying to go to an artist on a
PlaylistFile. This doesn't work as it's not an instance that has an artist, so,
only accept instances that have artist entries.
New build tools
Bump buildtools
Add play services voice search
Fix travis
Update korean translations
Music: Use smaller, more exact, constructors, fix NPE in getFullPath().

We received a crash report detailing a crash that occured due to a null
mFullPath field. This really shouldn't happen, but since it apparently does,
cover it with an if block like the rest of this class. This /could/ be fixed
with the constructor fix (detailed below); cover it up until possibly post-
release testing.

While looking into this bug, I also noticed the children classes for the Music
class are inexact constructors. For instance, we would construct the children
with getTitle() which is /not/ a getter. Use a better suited constructor and
change permissions so it won't happen again.
StreamHandler: Setup AudioAttributes for MediaPlayer.
MPD: Don't send a command queue if nothing was added in add().

We received a automated crash response due to an attempt to send an empty
command queue. This was due to a user doing an add() with very specific
parameters which would negate every conditional on the way through and
never added to the command queue. For this case, I've added a conditional
which should be negated if there is an empty command queue at the end.
Updated some German strings and compared with English strings.xml
changed tab to 4 blanks
corrected some hyphen