Modify "text" Block Attributes in a Pop-up Window

As a control engineer, I want to modify textual block attributes, so that I can send modified values to the PandAbox.

#### Acceptance Criteria
1. modifiable "text" attribute values are rendered as input fields.
1. I can type a new value in the value field of each attribute
1. On pressing the Return key, the modified value is sent to the PandAbox.
1. While waiting for a response from the PandAbox, the status icon spins
1. On receiving a response, the pop-up window updates the status icon

#### Notes
1. "text" means a modifiable string (as distinct from a label), which could represent textual or numeric data.
1. The validation of the entered value is performed by the PandAbox.
1. The status icon should reflect the status returned by the PandAbox.
1. The PandAbox may return an extended error message, which could be displayed as a tooltip (or similar).
1. Validation is done by the PandAbox. How should we report values/status to the user?
1. after user has entered a new value, but while we are waiting for PandAbox to respond?
1. how does the user know what value the server holds?
1. presumably, if the user types an invalid value, the server won't update its value.
1. if the user doesn't correct an invalid value, should it (eventually) get over-written with the server's value?