Reconfigure and extend Maxima menu under Insert

[mkraska]

Menu structure

Insert> Maxima> Settings:

• Takeover
• Restart
• Cleanup

Insert> Maxima> Install Maxima:

• Installation/Update
• Path to Maxima
• version information

Buttons for execution of MaximaControl (either as direct execution or as insert of command to canvas)

Restart (Callout: New Maxima session)
Cleanup (Callout: Reset variables)