Adding Installer package

[Conjuro]

Resolves #32.

There will be three separate packages, streamlink-twitch-gui, streamlink-twitch-gui.portable, and streamlink-twitch-gui.install.

For legacy reasons default package will be using the zip files, otherwise it's likely to mess up existing installs.

• streamlink-twitch-gui.portable: Old method of installing. "Streamlink Twitch GUI" folder renamed to "streamlink-twitch-gui.portable" and nuspec updated to reflect new package name/id.
• streamlink-twitch-gui: Old package. Install and uninstall scripts removed, dependency changed to "streamlink-twitch-gui.portable".
• streamlink-twitch-gui.install: New method of installing. WIP.

ToDo:

• Move "Streamlink Twitch GUI" folder to "streamlink-twitch-gui.portable"
• Create "streamlink-twitch-gui" and "streamlink-twitch-gui.install" folders.
• Copy nuspec to new folders.
• Change "id" (package name) in nuspec of ".portable" and ".install" folders.
• Update example in nuspec(s) to reflect new "id".
• Change dependency in default package nuspec to point at "*.portable" package.
• Review install and uninstall script to determine whether new package id in "*.portable" will require changes. (Is there a use case for both portable and install to be installed at the same time?)
• Create install and(?) uninstall script(s) for "*.install" package.
• Create streamlink-twitch-gui.portable package on Chocolatey, and upload nuspec.
• Upload streamlink-twitch-gui nuspec. Has to be done after "*.portable" package is active, and probably best to wait until next release of Streamlink Twitch GUI to avoid messing with version numbers.
• Create streamlink-twitch-gui.install package on Chocolatey, and upload nuspec.
• Add maintainers to all Chocolatey packages.
• Get new packages approved for automated validation. What's the process?

This is WIP, and will be done as I find time and energy.
I branched of the "Meta" branch (see #37) by mistake, and will wait until it's merged into "published" before rebasing rather than mess with it now and have to deal with the copied files.

[scowalt]

Awesome work!

One thing to consider: is there any functionality that's missing in the portable install? For example, URL protocol handlers? (I believe the PATH environment variable is updated anyways in the portable version)

If there are any functional disadvantages to the portable version, you may want to consider making the "install" version the default or pointing out the differences in the package description.