fix: sanitize Makefile

[vmarchese]

fix the following:

• remove " from the variables (e.g.: JR_SYSTEM_DIR="/Library/Application Support") and change the lines using it accordingly
• check the Windows var for AppData (e.g. APPDATA or APPADATA)
• define the JR_xxx_DIR with a /jr at the end (e.g: JR_SYSTEM_DIR=/Library/Application Support/jr) and avoid appending it when used