Some changes to workspace list and bookmark list

The main changes are listed following:

• Change bookmark list as files bookmark.

• Change workspace list to show all workspaces of all projects that had been added.

【 And sorry for retabing some vim-files making it difficult to read the diffs. :( 】

@yehuohan Many of the changes in this PR are great ideas. Overall this PR will need to be split up into smaller chunks, some of which are now in progress (in other ways) and have issues. There are a few I've mini-hacked on my end to make it work (e.g. the projects all stored together).

@yehuohan : Thank you very much for all the great work. Would you mind documenting the commits, for example, what Change bookmark list as files bookmark, is about, and splitting the pull request up into feature branches / PRs? @jyscao Or do you prefer cherry picking?

Thanks @yehuohan , is this now ready ?

@Konfekt Unfortunately I have to to say that I don't plan to do that, because I don't have much time on vim-ctrlspace now (and actually I use popc now). This PR was done at my start time with using git-pr and learning vim. So the commits aren't so beautiful and reasonable. Regret for this. If you want to provide what this PR does for vim-ctrlspace, I think it's better to rewrite this PR with new features of neovim/vim like floating window, popup and json. Finally, thanks vim-ctrlspace and all its contributors. :)

Your popc forks looks very interesting, as it uses LeaderF or Fzf instead of the custom built binaries which seem slow on Microsoft Windows. It seems that one cannot switch between different layer views such as buffers and workspaces if I read the documentation correctly (whereas in CtrlSpace that would be achieved by hitting w as workspaces)

• popc doesn't support any fuzzy search works (I'm not good at those algorithms). So popc just provides file paths or root path for other plugins like fzf, leaderf and telescope.
• popc supports switching between layers you want with bindCom