General improvements in the sign-in pages

The structure and look and feel of the different sign-in pages have diverged and need some love and care. A few improvements I suggest:

• Remove unnecessary classes
• Make elements Pajama compliant
• Simplify horizontal and vertical spaces
• Harmonise internal markup structure
• Unify language
• Unify look

Example #1: different headers and look of the buttons:

Sign-in page	Admin mode
	In addition, it doesn't look nice where the two borders meet

Example #2: different look of button and remember me checkbox:

Screen_Recording_2023-05-24_at_13.59.17

Example #3: when new redesign is enabled, page layout is different for sign-up page and trials sign-up:

Sign-up	Trials sign-up
	Alignment of the captcha is different and header on top.