issues #462

[piznel]

Gladys Pull Request check-list

To ensure your Pull Request can be accepted as fast as possible, make sure to review and check all of these items:

• [N/A] If your changes affects code, did your write the tests?
• [N/A] Are tests passing?
• Is the linter (eslint) passing?
• [N/A] If your changes modify the API (REST or Node.js), did you modify the documentation?

NOTE: these things are not required to open a PR and can be done afterwards / while the PR is open.

Description of change

Fix issue #462 and the following bugs :

• if the devicetype had no name,'undefined' was displayed
• the navigation buttons did not work properly if we were in real-time data display.
• the addition of a real time value drew a straight line between the first point of the graph and the last point.
• adding a real time value added it to the graph even if we displayed a curve in the past.