Add 32x32 icon, fix #112, fix #115, fix #117

[gabor-udvari]

Icon:

• Icons added to the Settings and Magic Fields admin page
• The wand-hat icon is Yusuke Kamiyamane's work from the Fugue Icons pack. It is CC-BY-3.0, so we can use it, but Yusuke has to be credited
• images/wand-hat-32-orig.png is the original icon made by Yusuke
• images/wand-hat-orig.xcf is the GIMP source, it was converted from Yusuke's PSD
• images/wand-hat.svg is made by Gábor Udvari in Inkscape
• images/wand-hat-32.png is exported from the SVG

Custom post type label suggestions:

• Plural and singular support was added

Readme.markdown:

• Fixed bad grammar
• Yusuke Kamiyamane credited

Fix #112:

• Fix jquery.stringToSlug.js to get rid of undefined error messages.
• This fix was also committed to the original repository of the stringToSlug plugin, so check for updates: https://github.com/leocaseiro/jQuery-Plugin-stringToSlug

Fix #115:

• The apostroph (') was only escaped in the custom field type description
  it is now escaped everywhere.
• Add the settings link to the plugin list page.

Fix #117:

• When the main editor is disabled the multiline field buttons are broken. Updated the admin/mf_post.php to fix this.