radar chart model implementation - in progress
adds radar chart
Radar chart finished
adds Radar chart constructor
adds Bubble chart model implementation
rename ChartXAxis and ChartYAxis classes names and add add toString() method
implement x and y axis for Radar charts and fix some errors
adds Filter Model
change the structure of the y-axis of the Bubble and Radar charts and fix issues with the Bubble chart
add Radar chart in Chart class
add empty constructor for CoreFilter
Update filter.xml name
comment filter root tag in Filter class
Merge branch 'develop' of https://github.com/AhmedShafei/HRForecast-WFM into Feature-graphs-main-layout

Conflicts:
	WorkForceManagement/src/de/hrf/workforcemanagement/model/Chart.java
	WorkForceManagement/src/de/hrf/workforcemanagement/model/ChartAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/model/ChartXAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/model/ChartYAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/model/TestSerializer.java
	WorkForceManagement/src/de/hrf/workforcemanagement/models/ChartAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/models/ChartXAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/models/ChartYAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/models/StandardChartAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/models/StandardChartXAxis.java
	WorkForceManagement/src/de/hrf/workforcemanagement/models/StandardChartYAxis.java