Add local/remote ICE candidates to current/pending description.

[LVala]

Thanks to this changes, session description obtained from pending_local_description() etc. will contain gathered/applied ICE candidates.

Adresses #80

[codecov[bot]]

Codecov Report

Merging #83 (34198ba) into master (348bd92) will decrease coverage by 0.23%. The diff coverage is 45.83%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #83 +/- ## ========================================== - Coverage 89.03% 88.80% -0.23% ========================================== Files 31 31 Lines 1395 1411 +16 ========================================== + Hits 1242 1253 +11 - Misses 153 158 +5 ``` | [Files](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/83?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc) | Coverage Δ | | |---|---|---| | [lib/ex\_webrtc/sdp\_utils.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/83?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9zZHBfdXRpbHMuZXg=) | `90.62% <100.00%> (+0.22%)` | :arrow_up: | | [lib/ex\_webrtc/ice\_transport.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/83?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9pY2VfdHJhbnNwb3J0LmV4) | `76.92% <50.00%> (-4.90%)` | :arrow_down: | | [lib/ex\_webrtc/peer\_connection.ex](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/83?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc#diff-bGliL2V4X3dlYnJ0Yy9wZWVyX2Nvbm5lY3Rpb24uZXg=) | `87.14% <36.84%> (-0.51%)` | :arrow_down: | ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/83?src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/83?src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). Last update [348bd92...34198ba](https://app.codecov.io/gh/elixir-webrtc/ex_webrtc/pull/83?src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-webrtc).