feat(interruptsource): allow interrupts to use an ssr option

[moribvndvs]

ssr option instructs interrupt sources to ignore targets
derived from global context such as window or document so
they can be safely used in ssr/universal apps.

If you are using ssr/universal, do not use
DEFAULT_INTERRUPTSOURCES. Instead, use
createDefaultInterruptSources({ssr: !isPlatformBrowser(platformId) }).
See docs or https://stackoverflow.com/a/46893433/64750
for information on how to use isPlatformBrowser.

Fixes #77, #115

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/HackedByChinese/ng2-idle/blob/master/CONTRIBUTING.md#pr
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior? (You can also link to an open issue here)

No support for SSR/Universal apps.

What is the new behavior?
Adds an opt-in option when creating interrupt sources that will allow compatibility with SSR/universal.

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[x] No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[coveralls]

Coverage remained the same at 100.0% when pulling ca8d68b on ssr into db0148b on master.

[bfwg]

I'm still getting the below compile error when I import NgIdleKeepaliveModule.forRoot() in the app.module of my Angular project, and run the command npm run build:ssr && npm run serve:ssr.

/Users/bfwg/code/ng2-idle-example/dist/server/main.js:112377
            : document.documentElement;
              ^

ReferenceError: document is not defined
    at new DocumentInterruptSource (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:112377:15)
    at createDefaultInterruptSources (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:112522:9)
    at Module.evxF (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:112527:34)
    at __webpack_require__ (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:20:30)
    at Object.V7fC (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:97581:13)
    at __webpack_require__ (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:20:30)
    at Object.K011 (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:86964:37)
    at __webpack_require__ (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:20:30)
    at Object.0 (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:437:18)
    at __webpack_require__ (/Users/bfwg/code/ng2-idle-example/dist/server/main.js:20:30)

main.js:112377 points to this line.

[moribvndvs]

Can you publish this example code somewhere?

[bfwg]

I made a ssr boilerplate app https://github.com/bfwg/ng2-idle-ssr-example.
Steps to reproduce:

1. clone the ng2-idle-ssr-example app.
2. npm install
3. build core and keepalive module from thie PR.
4. cope them into the node_modules of the boilerplate app, inside @ng-idle
5. run npm run build:ssr && npm run serve:ssr command.

Please let me know if you need more information.

[metsehaf]

@bfwg, did you find a solution to your problem? I am having similar errors to yours.