Suggest not to register `themePath/components` by default

[meteorlxy]

Feature request

For version: 1.0.0-alpha.1

What problem does this feature solve?

All .vue files in themePath/components are registerd as global components by default:

vuepress/packages/@vuepress/core/lib/prepare/AppContext.js

Lines 120 to 125 in ace3aec

	.use('@vuepress/register-components', {
	componentsDir: [
	path.resolve(this.sourceDir, '.vuepress/components'),
	path.resolve(this.themePath, 'components')
	]
	})

Theme makers may not want to register global components, but still want to have a components dir in the root path of their theme. (As I did in my own theme based on vuepress@0.x)

How should this be implemented in your opinion?

In my opinion, theme makers should use @vuepress/plugin-register-components themselves to control global components registration.

So I propose to remove line 123 above, i.e path.resolve(this.themePath, 'components'), and use another @vuepress/plugin-register-components in @vuepress/theme-default.

Are you willing to work on this yourself?**

Yes if admitted

[ulivz]

It makes sense, removed it at 4e8da95.