Lightline should not save &tabline when not enabled

[danhorner]

Thanks for your work on lightline. Documentation is great and I like the simplicity.

• I've disabled the tabline in favor of another plugin using g:lightline.enable.tabline=0
• But I have autocmds that change the color scheme when I switch from dark to light. I found that I needed to call lightline#enable() to pick these up.
• When I do this, or when I disable lightline, it caches a stale value of &statusline and then restores the stale value over my carefully constructed status line.

1. Is there a better way to update colors on color scheme change?
2. If not, would you be receptive to a patch to lightline that only stores s:_statusline and s:_tabline when those features are enabled?

 autocmd ColorScheme onedark let g:lightline.colorscheme="jellybeans" | call lightline#enable()
 autocmd ColorScheme mayansmoke let g:lightline.colorscheme="Tomorrow" | call lightline#enable()

[itchyny]

call lightline#colorscheme() | call lightline#update() is recommended way to do after changing colorscheme.