[desktop] Add babel support

Summary:
Manually calls babel and transforms files. First step towards webpack support.

It currently transforms all files in src/ and moves them to dist/. This means that absolute paths pointing inside src/ won't work which isn't ideal will be fixed in the future when webpack will be working.

Test Plan:

• Test if development version works (yarn dev)
• Test if prod wersion works (yarn package)

Reviewers: tomek, atul, ashoat

Reviewed By: tomek, ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5735