[bisq-network/bisq] Prevent memory leak in CandleStickChart & VolumeChart (#3914)

[Steven Barclay]

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Ensure that the superclass methods `XYChart.removeDataItemFromDisplay` and `XYChart.removeSeriesFromDisplay` are always called from the implemented `dataItemRemoved` and `seriesRemoved` methods respectively, as specified by the API javadoc.

This prevents a leak of old `Candle` and `VolumeBar` objects every time the trades charts view is updated. The former is quite substantial, as each Candle object has a retained size of about 70kB and there are up to 90 candlesticks / volume bars leaked per chart update.

--

By cycling through the _Month_, _Week_ and _Day_ interval a few dozen times, the following heap usage stats were obtained using JProfiler:

![Screenshot from 2020-01-22 10-42-19](https://user-images.githubusercontent.com/54855381/72887622-fd2cf680-3d03-11ea-9404-9e97f04a74a1.png)

I believe updates to the two charts happen periodically as long as the trades charts view is selected, as it appeared to leak while unattended as well. I haven't had a chance to measure the rate, though.
You can view, comment on, or merge this pull request online at:

  https://github.com/bisq-network/bisq/pull/3914

-- Commit Summary --

  * Prevent memory leak in CandleStickChart & VolumeChart

-- File Changes --

    M desktop/src/main/java/bisq/desktop/main/market/trades/charts/price/CandleStickChart.java (17)
    M desktop/src/main/java/bisq/desktop/main/market/trades/charts/volume/VolumeChart.java (23)

-- Patch Links --

https://github.com/bisq-network/bisq/pull/3914.patch
https://github.com/bisq-network/bisq/pull/3914.diff

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