Added compatibility with Color Scheme Solarized plugin and ST3

I've added compatibility with the Color Scheme Solarized plugin while retaining the possibility to use the default Solarized theme. Also tweaked the code to work with both ST2 and ST3.

If the Color Scheme Solarized plugin is present, then pressing F12 will switch between the themes from the plugin. If the plugin is absent, then pressing F12 will fall back to switching between the default Solarized themes.

I've tested the changes in the following situations and it worked correctly in all cases:
OSX: ST2 and ST3
Windows: ST2
Ubuntu: ST3