Improved UI

[easylogic]

• [x] clean white theme
• [x] create page tab panel
• [x] layer and images left panel
• [x] background-blend-mode, mix-blend-mode, filter is left 2 panel with background-color sets
• [x] Only one page editor
• [x] Layer, Image Lock
• [x] new design Property view (slider, input, number, select, custom ui property)
• [x] more bigger Canvas
• [x] remove layer preview panel
• [X] unit convertable slider ui
• [x] image url type
• [x] blend/filter preview performance improvement
• [x] support SVG icon
• [x] save current layer
• [x] save current page
• [x] save current color
• [x] save current background
• [X] Support conic gradient
• [x] support static color step ( when static step is checked, a 10%,b 20% -> a 10%,b1 10%, b 20% )
  • gradient has static color step
  • implements cut step
• [x] Support color step length (ex: px, em )
  • [x] change unit in gradient step ui
  • [x] change unit in gradient input