plugin: remove unused plugins

BufOnly, grep, supertab, wintagexplorer

Signed-off-by: Danny Huang <dahuang@nvidia.com>
plugin: minibufexpl: update minibufexpl

Signed-off-by: Danny Huang <dahuang@nvidia.com>
vimrc: SrcExpl: update setting of SrcExpl

Signed-off-by: Danny Huang <dahuang@nvidia.com>
vimrc: quickfix: add hotkey for quickfix

Signed-off-by: Danny Huang <dahuang@nvidia.com>
vimrc: minibufexpl: update settings

Signed-off-by: Danny Huang <dahuang@nvidia.com>
vimrc: add hotkey to switch between different window

Signed-off-by: Danny Huang <dahuang@nvidia.com>