ChartUnit.java: 
Removed createBarRenderer(...) method and references to this method. 
ChartUnit class now uses createAreaRenderer(...) method for rendering
the TIC graph.
Merge branch 'master' of https://github.com/CTMM-TraIT/trait_proteomics_qc_tool.git
Merge pull request #41 from FreekDB/master

ReportUnit: logger is no longer used
Merge pull request #42 from FreekDB/master

ReportUnitTest: added SORT_KEY_MAX_INTENSITY
Working on new requirement: Export selected reports in PDF format
together with metrics values and TIC graph.

Using itextpdf (www.itextpdf.com) for exporting reports in PDF format. 
Downloaded and added itextpdf-5.4.3.jar in lib directory. 
pom.xml: Added a new dependency itextpdf (version 5.4.3).
Created new class ReportPDFExporter.java to build and save PDF file from
the report unit (In progress - added list of TODOs).
ViewerFrame.java: Added menu item "Export Selected Reports as PDF" and
corresponding action handler. 
DataEntryForm.java: Added new method displayPDFDirectoryChooser() to
select location for saving PDF report file.
Constants.java: Added useful constants.
ReportPDFExporter and ViewerFrame: fixed some Checkstyle issues

ReportPDFExporter:
- Removed unused imports and logger.
- Added text and TODOs to Javadoc.
- Removed MalformedURLException from throws clause of the exportReportUnitInPDFFormat method since it is already covered by IOException.
- Shortened a few lines.

ViewerFrame:
- Added TODO: adjust reportCount for exceptions that occurred?
- Split of code for pdf export from the handleMenuActions method to the new handleExportPdfCommand method.