Fix several issues

[DanTalash]

This should fix several problems with the library.

• Issue #276 is a problem with callbacks not being functional when the library is used as a component.
  • The issue is that the scope is set incorrectly to a child scope instead of the correct scope where the callback function is defined.
  • This commit fixes the problem. Below is my comment from the issue page with examples showing the issue.
    • See this plunkr for an illustration of the problem. Note that while the callback function fires, the text doesn't update because in the called function this refers to the wrong object.
    • Here is a copy of the above plunkr with the issue fixed in the library. Note that when the callback is fired, this now refers to the correct object.
• Issue #298 is a problem with the mFormat filter where timezones are not applied if a moment object is not passed to the library.
  • This commit will also fix all tickets (#319, #270, #310, etc) asking for a way to have an empty input field when the user has not yet selected a date.

[DanTalash]

@eralha and @g00fy-, there appears to be quite some delay with getting PRs merged. Do you guys need anybody to help maintain this repo? I am willing to help.

[ovaldi]

@eralha and @g00fy-, there appears to be quite some delay with getting PRs merged. Do you guys need anybody to help maintain this repo?

+1