Need to support dangling spaces for a11y strings

[zepumph]

From a11y string conversion in phetsims/rosetta#193.

We have some strings that purposefully end/begin in spaces. Currently this feature is only on a branch, but there should be an issue devoted towards fixing this. Right now the string plugin will trim the strings for us.

[zepumph]

The first thought I have here is perhaps we should make these purposeful spaces a special char, maybe a unicode space that trim doesn't strip out.

[zepumph]

It would be good to note #619 in this discussion, since that issue is why trim calls were added.

@samreid and I discussed and we expect that this constraint will be easy enough to get around by rethinking the template strings. After reading in #619 I think it is not worth trying to support this. Over in phetsims/rosetta#193 we will make sure that when a11y strings are moved into json files, that they are audited for dangling white space.