Drive: pass commandline options to OS X launch agent program arguments

Currently at startup, Drive registers itself as a launch agent but the command line options are not passed to this agent, therefore at next startup the program will be launched with the default options.

We should propagate thes options to the launch agent, which can always be edited afterwards if needed. A typical use-case is to increase the sync delay and max-sync-step with:

open -a /Applications/Nuxeo\ Drive.app --args --max-sync-step=1000000 --delay=60

which should result in the following ~/Library/LaunchAgents/org.nuxeo.drive.plist file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>org.nuxeo.drive.agentlauncher</string>
  <key>RunAtLoad</key>
  <true/>
  <key>Program</key>
  <string>/Applications/Nuxeo Drive.app/Contents/MacOS/Nuxeo Drive</string>
  <key>ProgramArguments</key>
  <array>
    <string>--max-sync-step=1000000</string>
    <string>--delay=60</string>
  </array>
</dict>
</plist>

This should be quite easy to achieve by passing the commandline options to startup.register_startup().

This is related to NXP-13677 as we also want to not systematically reset the launch agent when (re)starting Drive.

Note that we should study the equivalent Windows implementation.