[NEW][WIP] Add Jitsi component

[Dnouv]

This PR adds a new Jitsi component using Jitsi's React SDK
Here is a screenshot of the demo page,

Thank you!

[lgtm-com]

This pull request introduces 2 alerts when merging 4e0ff01 into 0930180 - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class

[Sing-Li]

Hi @Dnouv Thanks for the PR. A lot of this work has actually been done, as part of the virtual conference coming up - in the "Greenroom".

See https://github.com/RocketChat/RC4Community/blob/master/app/pages/virtualconf/greenroom/index.js#L5

Please see if you can "tune this component" to the following:

1. Anyone with access to /greenroom will see one another as in a regular Jitsi conference
2. Set the component to "Live Stream" to an rtmp forest

Adding the two above will allow us to conduct the Alumni Summit with RC4Community.

[lgtm-com]

This pull request introduces 1 alert and fixes 1 when merging a078def into 637ede7 - view on LGTM.com

new alerts:

• 1 for Unused variable, import, function or class

fixed alerts:

• 1 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 3 alerts when merging 6cb0fb3 into 54d6bbd - view on LGTM.com

fixed alerts:

• 3 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 5 alerts when merging 0334966 into be23250 - view on LGTM.com

fixed alerts:

• 5 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 5 alerts when merging 17ee690 into 7d80e8f - view on LGTM.com

fixed alerts:

• 5 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 5 alerts when merging 8cbdd50 into 8651407 - view on LGTM.com

fixed alerts:

• 5 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 5 alerts when merging f95f259 into 8651407 - view on LGTM.com

fixed alerts:

• 5 for Unused variable, import, function or class