MPD: Fix album artist response key case.
MPD: Refix album artist stuff.

This commit (finally) removes the setAlbumArtist hack, if a album artist is to
be set in the track there has to be new construction due to the
equality/hashcode general contract. This fixes the broken album listing.
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.
Updated some German strings and compared with English strings.xml
changed tab to 4 blanks
corrected some hyphen
Merge pull request #650 from MaDill/master

Updated some German strings and compared with English strings.xml
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
NowPlayingFragment: Only set rating visibility on init, connection and config.

Setting the rating visibility was happening per track change, now we only
change it on initialization, connection and if the config option changes.
UpdateTrackInfo: Only attempt rating retrival if the config option is set.