[rfc][icedtea-web] Certificate viewer cleanup

[Jacob Wisor]

* Replaced old insufficient certificate viewer's action buttons handling with proper handling
* Made System-level certificates managable if current user has write access to a KeyStore (usually only root or admin)
* Added informative tool tip to disabled buttons when certificates are unmanagable
* Made certificate table uneditable
* Made certificate info table uneditable
* Made certificate info's descriptive JTextField have the same font size as its info table for better readability
* Added certificate file filters with Windows/Linux preference
* Added auto-suggested certificate file names when exporting
* Added automatically generated mnemonics
* Made labels link to corresponding JComponents
* Added a border to certificate type label for better readability
* Uniformed border sizes
* Added removing of multiple certificates at once
* Turned some only once occuring fields into static
* Added proper exception handling when setting system look & feel, hence removed superfluous "throws Exception" from method signatures

Happy reviewing!

Jacob