Implementation of Doughnut-chart for displaying number of publications/year

Closes #77 (closed)

Checklist:

• Make a doughnut chart according to discussed designs

The following feature from issue #77 (closed) has been achieved:

• Created Doughnut-chart for displaying publications per year for an author
• The color of bar charts giving information on the number of citations and the year of publication of a research paper is changed, as well as a new pie chart is added to give more insights into a researcher's performance visually.
• Hovertext labels and inside/outside labels with titles and display are added to have a more clear view.

The front end includes a bar chart and doughnut chart for visualizing the number of citations and publications per year of an author.

Here are the snapshots: