NGO Admins management

[aniri]

Add a new page /ngos/admins.

UI available here: https://www.figma.com/file/61NHR7fwmV1Dsv4Pb6F8T7/code4ro_mv_user-management_2018.04.21-(Copy)?node-id=754%3A0

depends on https://github.com/code4romania/monitorizare-vot-ong/issues/203

There are two types of admin accounts: organizer and regular (based on the organizer flag from the ngos table). The organizers will see the NGO page in the top menu and navigate to the ngo admins pages by clicking on the number of ngo admins from the ngos table. The regular admin should see directly the NGO Admins link in the top menu.

There is no specific UI for this page, but is very similar to existing UI (for NGO table):

• the page should show a table of ngo admins, without a filter or pagination
• for each admin it should show their name and available individual actions dropdown (there is no need for selecting multiple entries from the table)
• the available actions should be delete and edit
• there should be an Add NGO Admin button at the top of the table
• clicking on the add ngo admin button or on the edit action for an admin should open a new page with a simple form (similar to the one for adding an observer). The form should only have two input fields for name and password

_Please use bootstrap classes as much as possible and avoid adding custom css styles to keep the codebase clean & consistent. The new UI should be as similar as possible to the one in figma, not pixel perfect.

Also, make sure all texts are extracted in translation files._