First commit of masterlist converter.

This will be a separate program to BOSS that will convert a v2
masterlist to a v3 masterlist, and display error messages for any issues
found.
Fixed bad error message.
Fixed issue #42.
More libespm-related changes.
Build stuff. Improved Windows support, tidied up.
Sorting tweaks.

* Removed unused functions.
* Tidied up edge addition.
* The plugin graph now stores plugin properties directly, rather than
pointing to plugins in an external container.
* The plugin graph is now used to hold the installed plugins from the
beginning of the sorting process. The plugins list is still built up in
case sorting the graph fails.
Tidied up plugin reading, removed extra delete causing crashes.
Fixed issue #51.
Corrected file URL used in viewer.
Minor code cleanup, logging improvements.
Fixed plugins being loaded twice.
Fixed typo causing graphs to never be generated.
Fixed potential crashes when reading previous report.
Fixed bug in message language selection in metadata editor
Added ability to export plugin metadata as plain text from GUI.
Removed unnecessary plugin loading during metadata editor initialisation.
Changed metadata export functionality.

Now it just copies the text to the clipboard, instead of displaying the
text in a new window.
YAML generator now skips plugins with no metadata.
Forgot that metadata editor also displays existing plugin Bash Tags.
Readme update.