Truffle Grower 4+

Enhancements to the way historical data is visualised in the orchard views, including:
- optionally fade out old truffle locations on the map by increasing age
- allow users to see historical data using the orchard map
- add a new configurable truffle location report

Fade Older Truffles:
An option has been added to "Fade older truffles". When switched on, older truffles will appear faded in the map view.
The most recent/current seasons truffles will be shown as normal.
Truffles from previous seasons will be partially transparent - you can still see them on the map, but they will be fainter than the current truffles.
The older the truffles are, the fainter they will be shown on the map.

View Historical Data:
This enhancement allows a user to visually review changes to the orchard over time.
A "Display Date" field has been added to the orchard map view, allowing a user to select either a historical date or the value "now".
If a historical display date is selected, data shown in the truffle orchard view will reflect the state of the orchard on that date:
- Historical truffle and tree data will be shown as it was on the selected display date.
- More recent truffles and observation data will not be shown.
If the value "now" is selected the orchard view shows the most recent truffles and observations.

Truffle Location Report:
A new truffle location report makes it easy to track changes to where truffles have been found in the orchard over a number of seasons.
When requested, a configurable Truffle Location Report is generated as a pdf file. The truffle species, colours and date ranges to plot are all configurable.