[wip] upgrade to netstandard and rx 3.0 bits

[ghuntley]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Feature

What is the current behavior? (You can also link to an open issue here)

Profile78 based library that uses Rx 2 bits.

What is the new behavior (if this is a feature change)?

Netstandard v(undecided) library that uses Rx 3 bits.

Does this PR introduce a breaking change?

Yes, upgrading to rx3.0 bits and converting to netstandard which may imply dropping Windows 8, Windows Phone 8 and most definitely Windows Phone Siverlight.

Please check if the PR fulfills these requirements

• The commit follows our guidelines: https://github.com/paulcbetts/Fusillade/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

This PR is blocked until the following occurs:

• Upgrade ReactiveUI to netstandard and rx3.0 bits - Ship ReactiveUI 7.0 ReactiveUI#850 and use new rx bits in rxui v8 ReactiveUI#1123
• Upgrade Akavache to netstandard and rx3.0 bits - Adopt netstandard Akavache#308 and Upgrade Akavache to the new version of Rx Akavache#307
• Upgrade Punchclock to netstandard and rx3.0 bits
• Upgrade Splat to netstandard

[flagbug]

@ghuntley This file can be ignored

[musicm122]

FYI: Punchclock now uses the Rx3 bits
https://github.com/paulcbetts/punchclock
https://github.com/paulcbetts/punchclock/blob/master/src/Punchclock.nuspec