* Fix input files being overwritten by newly uploaded files
- Fix a bug that caused existing selected/uploaded files to be overwritten when a new input file is uploaded through input element.
- Add source property to change event to differentiate between uploaded files using input element and drag/drop uploads to avoid processing drag/drop files more than once, thus avoiding file duplication (file duplication resulting from copying drop/drop files to input files on each 'change' event).
* Dispatch and use file-input-change instead of change event for merging
- Dispatch "file-input-change" event after each "change" event in file upload, to notify other functions/components relying on the files provided by the \<input\> element.
- Use "file-input-change" instead of "change" event to display the latest version of uploaded files.
# FAQ:
- Why use "file-input-change" instead of "change" in merge.js?
= "change" event is automatically triggered when a file is uploaded through \<input\> element which would replace all the existing selected/uploaded files including the drag/drop files.
## Example:
Let's say that the user wants to upload/select the x.pdf, y.pdf and z.pdf all together:
- user selects "x.pdf" -> file selected successfully.
= selected files: x.pdf
- user drags and drops "y.pdf" -> file dropped successfully
= selected files: x.pdf, y.pdf
- user selects again using \<input\> "z.pdf" -> file selected succesfully overwriting selected files.
= selected files: z.pdf
