#28 implement context filter

[shumal1]

Please see commit log, closes #28

[shumal1]

@shizuko-akamoto Done addressing comments, let me know if it works.

[shizuko-akamoto]

@shizuko-akamoto Done addressing comments, let me know if it works.

Sorry, just a bit more styling issues:

1. let's remove the shadow effect on hover contextFilterSelectorEntry
2. The chevron up and down of selector look better if it's aligned to right side of the box Like this: Just move the justify-content: flex-start from .contextFilterSelector to .contextFilterSelectorEntry.
3. I realized after you extended .button and .contextFilterSelector in places, most of the stylings to on :hover and :active are duplicated. Removed them and the component still look the same.

(before u start getting annoyed LOL, here's a quicker fix, just copy + replace these in 😛)

.contextFilterSelector{
  @extend .button;
  border: 8px;
  width: 140px;
  padding: 0 1em;
}

.contextFilterSelectorEntry{
  @extend .contextFilterSelector;
  border-radius: 0;
  width: 140px;
  text-align: left;
  justify-content: flex-start;
}

.contextFilterSelectorList {
  list-style: none;
  padding: 0;
  margin: 0;
  background-color: $tc-white;
}

After those changes, I'm good with these two components.

[shumal1]

Done addressing comments.