Update macOS packaging for 10.15.4

Several smaller fixes to provide an improved handling of installing/using RT on macOS.
* mac: update entitlements for 10.15.4
* mac: fix the CLI. Provides an un-codesigned rawtherapee-cli outside the app bundle for use on the terminal command line, using the app bundle's 3rd-party libraries.
* How to install RawTherapee.app and rawtherapee-cli for macOS

tools/osx/rt.entitlements

@@ -1,19 +1,16 @@
 <?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
-    <dict>
-        <key>application-identifier</key>
-        <string>com.rawtherapee.RawTherapee</string>
-        <key>com.apple.security.temporary-exception.files.absolute-path.read-write</key>
-        <array>
-            <string>/</string>
-        </array>
-        <key>com.apple.security.cs.allow-dyld-environment-variables</key>
-        <true />
-        <key>com.apple.security.files.user-selected.read-write</key>
-        <true />
-        <key>com.apple.security.app-sandbox</key>
-        <true />
-        <key>com.apple.security.files.downloads.read-write</key>
-        <true />
-    </dict>
-</plist>
+<dict>
+	<key>com.apple.application-identifier</key>
+	<string>com.rawtherapee.RawTherapee</string>
+	<key>com.apple.security.app-sandbox</key>
+	<true/>
+	<key>com.apple.security.cs.allow-dyld-environment-variables</key>
+	<true/>
+	<key>com.apple.security.temporary-exception.files.absolute-path.read-write</key>
+	<array>
+		<string>/</string>
+	</array>
+</dict>
+</plist>