Add the killswitch and secure options to the manager

[Senyoret1]

Did you run make format && make check?
The go code was not changed. npm run lint and npm run build were used.

Fixes #609

Changes:

• A checkbox for activating/deactivating the killswitch option was added to the modal window used for configuring the vpn-client app. Additional changes were added to the modal window for being able to add the new configuration option independently from the server selection options.

• A checkbox for activating/deactivating the secure option was added to the modal window used for configuring the vpn-server app.

Note: changes mentioned in #609 (comment) are needed before finishing the PR.

How to test this PR:
Open the modal windows used for configuring the vpn-client and vpn-server apps and check:

• If the changes are correctly saved in the visor.
• If after opening the modal windows the UI shows the options checked or unchecked as appropriate, depending on the current configuration saved in the visor.

[Senyoret1]

The last commit includes the changes needed for the PR to work. I tested it and the configuration is saved in the visor, but I think the killswitch will only work after #608 is merged.

[jdknives]

@Senyoret1 good job. Works as expected.