Update manual input form

[aaronkim218]

Description

Removed bend extrusion field from manual input form. Send data from manual input form to manua_input_to_gcode executable as json string. im using nlohmann/json library to parse the json string. i included it in the project as a single header file under a new directory "backend/dependencies". i also changed the bend direction input field from a number to a string because manual_input_to_gcode expects bend direction to be something like "y+"

Fixes #42 and #46

How Has This Been Tested?

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Checklist:

• I have performed a self-review of my code
• I have reached out to another developer to review my code
• I have commented my code, particularly in hard-to-understand areas
• New and existing unit tests pass locally with my changes