Nemo

Bug Fix
* fixed an error when preferences are not defined

New features
* Added user preferences and added the option to receive ICS calendar invites (via user preferences) when creating and cancelling reservations

* Added a request parameter 'no_header' that can be used to hide the header on NEMO pages. for example "/status_dashboard/tools?no_header=true". This can be useful to display read-only information on screens outside the labs.

New features
* Added the ability to set times when policy rules should not be enforced for a specific tool (i.e. between 9pm-6am, don't enforce policy rules for JEOL E-beam, so users can reserve for longer or shorter periods of time etc.) policy rules can also be turned off during weekends.
* Added a direct link to tool status dashboard at /status_dashboard/tools

Security
* Updated Django version to avoid a security vulnerability

* Updated billing page to submit only on "Update" button click