More bug fixes!

Changes in this release:

• New: Install browsers remembers last browsed directory, and re-opens in it
• New: Add Apply button to the settings page - writes out any settings that have been changed, but does not close the settings page.
• Fix: mod list parse failure when "enabled_mods.json" file did not exist
• Fix: two more upgrade/replace bugs
• Fix: not being able to edit vmparams on first start (first time selecting Starsector installation directory)