Observation App - File upload functionality implemented

Now files can be uploaded in *edit view* of Observation App :
- For authenticated user's, there is appearance of upload button to upload files.
- User can select the file and upload it, then uploaded file's mime type will be displayed in the popup and name will be shown in tooltip.
- By clicking on file, browser supported formats will be opened in new tab of browser or else ask for download.
- Even user can remove file from list by clicking on ```x``` .


On landing page's popup (read view) :
- File/s are displayed in the popup.
- File's mime type will be displayed and name appears in tooltip.
- By clicking on file, browser supported formats will be opened in new tab of browser or else ask for download.