Deferring of offscreen images feature added.

[inomag]

Description

Added a new lazy loading feature for faster rendering of webpages containing several .jpg, .jpeg, .svg & .png files.

Fixes #78

Index.html Before
https://user-images.githubusercontent.com/66073063/103769825-00231300-504b-11eb-89b7-3e25412f6db2.mp4

Index.html After
https://user-images.githubusercontent.com/66073063/103770007-4aa48f80-504b-11eb-81a4-eb46de56b3bf.mp4

Similar changes are also done in team.html & event.html

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• Declared a new class .lazyload in images.
• Replaced src attribute with data-src which will be change into src once image is in viewport, hence rendering images only when they are in viewport.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings