Scan-GUI: Switching from simple to extended mode should keep the values for the common fields

Issue description:

• in Scan GUI, when user switches between various input modes (Simple / Extended / All) or between various scan configuration types (Relative / Absolute), the values already entered in the UI fields/inputs magically disappear.

Vocabulary: Hereinafter, "higher" level means the one with more fields available (i.e. All is higher than Extended and Simple is the lowest).

Desired solution:

• user-entered values should be persistent when switching between input modes or scan configuration types;
• when switching from "higher" to "lower" level input mode, all additional values have to be saved and restored on switching back;
• in any given mode (Simple / Extended / All), only visible values are used for scan configuration; for hidden values (e.g. tolerances in Simple mode) the default values are used;
• when switching from Relative to Absolute scan and back, no recalculation is done; last saved values for field size (in relative) and start/end (in absolute) are restored, alongside with number of steps and step size