New specifiers, grid definitions and minor style changes

[erikrakuscek]

• Added new specifier for bullet card block: 'no-card-border'
• Added new specifier for card block: 'content-top' which positions card content to the top
• Added new specifiers to carte blanche block: 'big-padding-content' and 'no-outer-borders'
• Added new specifier to enh heading block: 'align-middle', centers block vertically
• Added a gap between icon and preheading in enh heading block
• Added mx-auto to video to center it
• Added COMMON_GRID_1_COL and COMMON_GRID_4_COL grid definitions
• Removed gap from grid when using specifier 'style-table-borders'