Use consistent fields for JIDs and passwords and improve login page

* Validate entered JID and password
* Add show/hide button for password
* Disable connect button if JID or password are invalid
* Focus JID field after loading login page
* Focus field with invalid input if connect button is clicked or enter key pressed
9 jobs for refactor/fields in 23 minutes and 32 seconds (queued for 90 minutes and 2 seconds)
Status Job ID Name Coverage
  Test
passed #29029
allowed to fail
clazy

00:01:20

passed #29030
qmllint

00:00:26

 
  Build
passed #29033
archlinux

00:01:41

passed #29032
debian-sid

00:01:23

passed #29031
neon-bionic

00:01:29

 
  Deploy
passed #29036
allowed to fail
android

00:08:04

passed #29034
linux-appimage

00:11:46

passed #29037
allowed to fail
mac-osxcross

00:05:16

passed #29035
allowed to fail
windows-mxe

00:05:03