New Linux build

[terreng]

Figure out which combination of Linux builds to do. Make AppImage build to support auto update and consider making this the primary download.

Also:

• add linux file paths to logs and config.json pages
• Make sure metadata is all there (Originally posted by @terreng in Linux build #89 (comment))

[terreng]

@ethanaobrien It's hard for me to test with linux, so I'd appreciate your help getting all of the metadata right, including the taskbar icon as mentioned in #213. Also if you have any idea how to fix #172.

package.json is where all the metadata is specified, and you can take a look at the electron-builder documentation for help.

[ethanaobrien]

Sure, I can take a look when I get the time