[FEATURE] ability to edit ggplots

[AmeliaES]

allow user to edit ggplots, eg. colours, labels of axes, labels in legend.

[AmeliaES]

• change y and x axis limits
• change colours
• change x and y axis labels
• change legend title

[AmeliaES]

User can edit x and y axis labels and colours of lines in categorical variable plots (for the Interaction Variable page).
Bugs include:

• If the user changes interaction variable the plot colours are not reset (categorical only)
• if the user clicks on Customise Plot again the values are reset to default rather than the last chosen values (if any).