Various UI improvements

[adriengivry]

Description

• Inspector elements now keep the same column size consistently based on component type
• Changed "Add Component..." button style to default
• Table rows with only disabled widgets are now properly skipped
• Introduced AssetField
• Now using asset icons instead of "..."
• No more "Empty" string in asset fields
• Textures now also use AssetField, which also supports previews (so technically any asset type can display a preview)
• Components & behaviours can now be moved up and down in the inspector (re-ordered)

Related Issue(s)

Fixes #(issue number)

Review Guidance

Write here.

Screenshots/GIFs

"Add Component..." button doesn't visually yell anymore

Introduced AssetField, for a nicer looking input field for assets

AssetField is also used by the textures

Components can now be re-ordered (moved up and down)

Checklist

• My code follows the project's code style guidelines
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes don't generate new warnings or errors