Theia 1.16.0

See theia's [changelog](https://github.com/eclipse-theia/theia/blob/v1.16.0/CHANGELOG.md#v1160---7292021), we update from 1.13.0 to 1.16.0.

Changes specific to slapos port:
 * We set `warnOnPotentiallyInsecureHostPattern` because the new warning is very intrusive ... but it might actually be very insecure. For now we don't have solution. We are tracking this in https://erp5js.nexedi.net/#/bug_module/20210819-20614EE
 * New libsecret component that is now required by theia
 * Switch to using vscode git instead of theia git, to use timeline ( see https://github.com/eclipse-theia/theia/pull/7997 )
 * globally version up slapos.core to https://pypi.org/project/slapos.core/1.6.18/

See merge request nexedi/slapos!1039