Usability improvement: use default framework.iconSet to find icon by name (without prefix)

[mycarrysun]

Problem

Its very annoying to have to use the prefix of your preferred icon set. It also makes a refactor hard if you want to change all the icons across your app to another icon set.

I also understand if you have multiple icon sets included, you should have the ability to still choose which one to use in QBtn and QIcon etc.

Proposal

It would be nice to have QIcon look for an icon without the prefix, and if one is found for your icon set configured in the framework.iconSet it should use that icon instead of the material-icons by default.

Before

<q-icon name="sym_o_call" />
<q-btn icon="sym_o_call" />

After

<q-icon name="call" />
<q-btn icon="call" />

I'd be happy to put up a PR if this proposal is accepted.