Date pickers default to US date format: Change to use @material-ui/pickers library

**Is your feature request related to a problem? Please describe.**
The current (native) date pickers default to the US `mm/dd/yyyy `date format, whereas Sri Lanka generally uses `dd/mm/yyyy` or `yyyy/mm/dd`.

**Describe the solution you'd like**
With the use of `@material-ui/pickers` instead of native pickers, we can set the date format that we need (native pickers do not allow this according to [this thread](https://github.com/mui-org/material-ui/issues/10251)).

**Describe alternatives you've considered**
Using `@material-ui/pickers`, we can easily set the date format using the `dateFormat` attribute.

Start by locating the current native date-picker usage in the frontend and review how dates are currently formatted. Compare that usage with the @material-ui/pickers integration described in the issue; done means the picker supports a Sri Lankan date format such as dd/mm/yyyy or yyyy/mm/dd and the relevant date-entry flows continue to work.

Written by the indexing model from the issue text.