LegendEntry does not contain delete element when serialised
*Created originally on Bitbucket by [CharlieC](https://bitbucket.org/%7B32d660d5-f934-4ce5-a7b0-52750378fae1%7D/)*
The following class should include a delete tag when serialised
```
#!python
legendEntry = LegendEntry(0, delete=True)
```
```
#!xml
<legendEntry>
<idx val="0" />
<delete val="1" />
</legendEntry>
```
But the delete tag is missing.
issue