feat: Added alignment support for label headings

Label style headings can now be aligned left, center or right. They are
affected by the new textoff option.

Closes #124

fix!: Deprecated old presets

lua/definitions.lua

@@ -128,6 +128,9 @@
 --- Enable/Disable stylized headings
 ---@field enable boolean?
 ---
+--- Fallback textoff value
+---@field textoff? number
+---
 --- Number of characters to shift per heading level
 ---@field shift_width number?
 ---
@@ -145,6 +148,9 @@
 --- Name of the style to use
 ---@field style string
 ---
+--- Alignment for label styled headings
+---@field align? string
+---
 --- Default highlight group used by the rest of the options
 --- Used for highlighting the line when the style is "simple"
 ---@field hl string?