fix(umd): prevent inclusion of Vue in bundle

[Haroenv]

This is fixed in two spots:

1. add Vue to externals for the UMD (used in Panel)
2. use the Vue object passed to the install function instead of importing it ourselves (in the plugin)

Furthermore this also fixes the plugin which needlessly exposes all widgets (you can already import them easily, since the default export is being put on the window)

[francoischalifour]

This warning appears while building.

src/instantsearch.umd.js → dist/vue-instantsearch.js...
┌────────────────────────────────────────────┐
│                                            │
│   Destination: dist/vue-instantsearch.js   │
│   Bundle Size:  224.06 KB                  │
│   Minified and Gzipped Size:  57.93 KB     │
│                                            │
└────────────────────────────────────────────┘
(!) Missing global variable name
Use output.globals to specify browser global variable names corresponding to external modules
vue (guessing 'Vue')

[Haroenv]

good call, I didn't have it earlier, but can replicate now @francoischalifour

[Haroenv]

by the way, nice effect of this:

before

src/instantsearch.umd.js → dist/vue-instantsearch.js...
┌────────────────────────────────────────────┐
│                                            │
│   Destination: dist/vue-instantsearch.js   │
│   Bundle Size:  284.17 KB                  │
│   Minified Size:  281.05 KB                │
│   Gzipped Size:  79.27 KB                  │
│                                            │
└────────────────────────────────────────────┘

after

src/instantsearch.umd.js → dist/vue-instantsearch.js...
┌────────────────────────────────────────────┐
│                                            │
│   Destination: dist/vue-instantsearch.js   │
│   Bundle Size:  224.09 KB                  │
│   Minified Size:  221.15 KB                │
│   Gzipped Size:  57.93 KB                  │
│                                            │
└────────────────────────────────────────────┘

[francoischalifour]

Nice decrease!

[samouss]

It's better without Vue embed!