Add allinone (clean/vendor/build) default target to Makefile, Remove gui/providers/providers.json from git repo, Don't use unlink on *nix in Makefile

Fixes #867 (closed)

Makes developing a bit easier.

I removed the auto-generated providers.json from the repo. It seems like git also removed the upper directory. Seems like there was nothing else inside.... Nevermind: I had to change the gen-providersjson python script to create the directory....

branding/scripts/gen-providers-json

@@ -29,6 +29,7 @@ def generateProvidersJSON(configPath, outputJSONPath):
         providerData = getProviderData(p, config)
         addCaData(providerData, configPath)
         providers['providers'].append(providerData)
+    os.makedirs(os.path.dirname(outputJSONPath), exist_ok=True)
     with open(outputJSONPath, 'w', encoding='utf-8') as f:
         json.dump(providers, f, ensure_ascii=False, indent=4)