Add Digikam, closes #8

I am successfully able to build and run Digikam with this.

![screen shot 2013-12-17 at 13 47 25](https://f.cloud.github.com/assets/323761/1764219/b879a6ea-6722-11e3-9985-6c8ef094c04b.png)

Notes:

* Worked around #8 by using Digikam's internal KDE Graphics libs (`-DDIGIKAMSC_USE_PRIVATE_KDEGRAPHICS=on`). There are a [few other](https://github.com/tlvince/homebrew-kde/commit/d02c3156893f1ff89b52d8742a01cc6175395b89#diff-2069d1b8b203f3508c0f90400324452aR43) formulae to write if we want/need to support shared libs.

* A build error was thrown with regards to the panorama plugin (`'Unknown CMake command "FLEX_TARGET".'`). I tried using brew's newer version of flex (`depends_on 'flex'`) to no avail. I suspect we may also have to write a formula for [hugin](http://hugin.sourceforge.net). Disabling the plugin (via a [patch](https://gist.github.com/tlvince/8004513/raw/b61f7213d56058e7d97f00c0bfbf9701eea03aac/disable-panorama.diff)) works for now.