Add new relative tempo option in Tempo text inspector

Tempo text is used frequently at the beginning of a piece or at specific passages where there is significant tempo change.
But it is also used to create expression. Suppose you start at quarter note 120, then, for instance, you may create an agogic accent by setting tempo at 116 for just the accented note. Or you can create a rubato specifying a slightly different tempo for each note in a group.
However, if you then change your mind and decide that the general tempo is better at 112, for instance, then the whole set of subtle tempo changes you have input for the sake of expression will be messed up.

It is suggested that in the Tempo text inpector a new category, "Relative tempo", or "Relative", be included, which would be expressed as a percent change (positive or negative) relative to the most recently notated absolute tempo. A % sign would inform the user that it is relative tempo. Unlike absolute tempo, the change would hold only for the note to which it is applied.

Workaround: you can change the general speed of playback from the Play panel but 1) this affects the whole score, and it could happen that you want to change one section only; 2) The Tempo mark will still be 120, unless you make it read 112 and uncheck "follow the text" in the inspecctor.