Add UI elements to eyeControl to detect python and unoconv

 * The following changes are to the "Office Support" tab of "System" under "Administration" in eyeControl
 * If the path to python is a valid one, then the version is displayed. If not, then "Not Found" is displayed.
 * When the path is changed and saved, the new path is checked, and the message updated.
 * If unoconv is not detected in oneye's extras folder, a message is displayed.
Detection of failed convert and a 'please wait' message in eyeVisor

 * When eyeVisor is opened to view a file, a message "Rendering, please wait..." is shown until the conversion is complete
 * Should the conversion fail, this is now noticed and a message ("Conversion failed.") is displayed.
    - Whilst not exactly helpful for debugging, it is less disturbing to an end user than the actual PHP error itself
Improve eyeConverter

 * Before using unoconv and python to convert a document, eyeConverter will now check that the first is installed and it can find the second. If not, it returns false.
 * An alternate command to be passed to shell_exec has been provided, but commented out.
    - This alternate command tells unconv to use the oneye user's ./tmp directory as the HOME environment value for open/libreoffice, rather than the web server's home folder.
    - At the time of committing, this feature is not officially supported by unoconv yet (but hopefully soon will).
    - This feature should fix problems on CentOS and other systems where the web server does not have read/write access to its own home folder.
Change error message upon unoconv/python not being installed/configured

 * The new message is less specific and tells the user to contact the admin.
Redirect where submodule 'unoconv' points to

 * Having the submodule 'unoconv' point to a version that doesn't work for us is a little counter-intuitive
 * This commit changes the location from dagwieers/unoconv to s0600204/unoconv
 * In the event that Mr Wieers decides to merge my changes or write something himself that resolves the problem my changes address, we can always redirect the module back
Merge pull request #15 from s0600204/office