Add methods for increasing download speed

[gudarzi]

Add settings/methods for increasing download speed. For example:

• using parallel connections for downloading (let users decide how many connections to use)
• using HTTP_v2 and its features like multiplexing (multiple requests over 1 connection)
• increasing buffer size (it's 80kb for now)

[Day509]

Hi there ! my friend @AbdBoutchichi and I would like to contribute to this issue. If this one is available, we will be happy to work on it and be assign to it.

[Day509]

We look over this PR [#69] and we want to know if this issue is already done or not ?

[gudarzi]

@Day509 that pr has conflicts and it's not gonna be merged into the app.