frint-di: Fix Container.get() return type

[viacheslaff]

In practice Container.get() returns instance of a provider, which can be anything.

Provider interface is a definition of provider, not instance. Therefore typing was incorrect.

Make options optional in createContainer() definition

[fahad19]

may be a good time to make options (second argument of createContainer) optional too in typings.

[viacheslaff]

@fahad19, made options optional in createContainer() definition

[fahad19]

thanks!

not your doing in this PR, but the build is failing because of some linting issues:

/home/travis/build/frintjs/frint/packages/frint-react/src/components/observe.js
  7:28  error  Unable to resolve path to module 'frint-component-handlers/lib/ObserveHandler'  import/no-unresolved
  7:28  error  Missing file extension for "frint-component-handlers/lib/ObserveHandler"        import/extensions

/home/travis/build/frintjs/frint/packages/frint-react/src/components/Region.js
  6:27  error  Unable to resolve path to module 'frint-component-handlers/lib/RegionHandler'  import/no-unresolved
  6:27  error  Missing file extension for "frint-component-handlers/lib/RegionHandler"        import/extensions

/home/travis/build/frintjs/frint/packages/frint-react/src/services/Region.js
  1:27  error  Unable to resolve path to module 'frint-component-handlers/lib/RegionService'  import/no-unresolved
  1:27  error  Missing file extension for "frint-component-handlers/lib/RegionService"        import/extensions

[codecov[bot]]

Codecov Report

Merging #414 into master will not change coverage. The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #414   +/-   ##
=======================================
  Coverage   97.74%   97.74%           
=======================================
  Files         111      111           
  Lines        4251     4251           
=======================================
  Hits         4155     4155           
  Misses         96       96

Impacted Files	Coverage Δ
packages/frint/src/App.ts	99.35% <100%> (ø)	:arrow_up:

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[viacheslaff]

@markvincze, could you please take a look if these changes make sense to you as you were the one who ported Frint to TypeScript?