Add Functionality to UPLOAD code

[sirjan13]

Add a button to upload code from Local Machine. Currently allow only C,C++,Python files to be uploaded.Once the Code is uploaded it should display in the editor and the language should be auto detected.
Eg : if i upload a C++ file then language chosen should change to C++ and the code appears in the editor.

NOTE: Pull Requests should be backed with screenshots for the proposed chaanges failing which the PR wont be merged.