Fixed bookmarking behavior.
Theme switching implemented.

Added three additional themes.
Closes #1.

Squashed commit of the following:

commit a75f064b6cc2419132f05b2049045e25f5889672
Author: George Venios <veniosg@gmail.com>
Date:   Sat May 17 01:31:29 2014 +0300

    Changed the AB icon (logo).

commit 9c468097624e8bbb0686d484f073bf4138ec13db
Author: George Venios <veniosg@gmail.com>
Date:   Sat May 17 01:15:21 2014 +0300

    Fixed a bug where pathbar items would remain invisible on #cd() instead of animating.

commit 65dd0f6c2b9937f36735736e3b6b85754871c4d5
Author: George Venios <veniosg@gmail.com>
Date:   Sat May 17 00:50:05 2014 +0300

    Completed Grayscale theme.

commit cefbe3328286ae417533550e621f3b1058c86934
Author: George Venios <veniosg@gmail.com>
Date:   Sat May 17 00:11:55 2014 +0300

    Initial implmementation of Grayscale theme.

commit 5523c7485507482eb787e1f5f6c81e3396696b8f
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 23:15:12 2014 +0300

    Theme tweaks.

commit ecdb5d9c2bb9d9fcc7a565b4eb1296225e1d9f70
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 22:13:50 2014 +0300

    Added vanilla holo theme.

commit fb79b0b14edb04e276d07344ad734034355cde70
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 21:07:10 2014 +0300

    Compressed images.

commit 9a8407b592b46bffa1db04f166777977cada770b
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 19:42:35 2014 +0300

    Added and compressed list item icons for all themes.

commit c5e0e243272a9e98a1056da4e2d7c96d228d9a66
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 16:30:05 2014 +0300

    Fully implemented switching between themes.

commit a66c97b8539d1785a325c9c10f3218d6bf700666
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 12:52:49 2014 +0300

    Finalized Dark theme widgets' styling.

commit b93eb602ad5e9bf996aad4de9a8ed49b408f1397
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 04:02:38 2014 +0300

    Progressed on dark theme.

commit a81b06c1828f3e265b816e2d697ae96bc673338a
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 03:35:01 2014 +0300

    Theme fixes and tunings.

commit c4ff05e9575de4eee79c9205336f496f127dec6a
Author: George Venios <veniosg@gmail.com>
Date:   Fri May 16 03:05:56 2014 +0300

    Some theme related bugfixes and lots of dark theme fine tuning.

commit d77b2fbc5b46d0149f02f471e1aad9ad11dbaa40
Author: George Venios <veniosg@gmail.com>
Date:   Thu May 15 23:02:50 2014 +0300

    Implemented necessary theme attributes and applied initial values.

commit 861b3e7f8774716532c83bc36192401bf63ff48a
Merge: 683aebb 0045051
Author: George Venios <veniosg@gmail.com>
Date:   Thu May 15 21:00:31 2014 +0300

    Merge branch 'develop' into enh_1_themes

commit 683aebb0b637a8c90b66dadcdc2e2832b9608151
Author: George Venios <veniosg@gmail.com>
Date:   Thu May 15 20:58:07 2014 +0300

    Enabled windowContentOverlay.

commit 49218651a86b5a3badf125b2dfcbefb578b81137
Author: George Venios <veniosg@gmail.com>
Date:   Thu May 15 20:48:00 2014 +0300

    Migrated to PreferenceFragment. Closes #7.

commit f7115d21ca64f6470f1b512fa4c35811cc0dc2e6
Author: George Venios <veniosg@gmail.com>
Date:   Thu May 15 18:43:35 2014 +0300

    Implemented Theme switching mechanism for activities.

commit af0c6404f3d33f2f289cfe3528c872617615bd79
Author: George Venios <veniosg@gmail.com>
Date:   Thu May 15 17:30:43 2014 +0300

    Added placeholder second theme.