Generalize one-line installer

[5chdn]

AFTER: openethereum/parity-ethereum#8887

We have to rethink the one-line installer logic after we remove debian/centos pipelines.

Now, that libssl is not an issue anymore, I would suggest just looking:

IF system IS windows THEN
    GET parity.exe FROM windows
ELSIF system IS macos THEN
    GET parity FROM macos
ELSIF system IS linux THEN
    CHECK architecture 
    GET parity FROM linux AND architecture

I know you want to take this @fevo1971 :D

[5chdn]

This is actually independent from the PR linked above because the binaries are already existing.

[ddorgan]

@5chdn will do!

[fevo1971]

i just merged the new version of the installer script. because we no longer supply
distribution/os specific packages it installs only the parity-binary.

note:
if parity releases where maintained via a package-manager (like rpm, dpkg or pkg on mac)
in the past, it's a good idea to uninstall the parity package manualy before executing
get-parity.sh.

[5chdn]

I'll add this to the release notes. Thanks!