Add support for Cmd-F

[sffc]

Feedback from Fabien:

Is there a chance that you could add a search feature with the Cmd-F keyboard shortcut? I like to use the search feature when writing code, and I miss it a lot in Card Creatr Studio.

[sffc]

Fabien followed up:

a specific example showing you concretely how it would prove very helpful: after any important change in the template pane, I immediately check out the impact/result on the card display. Since I have a small 13'' McBook screen, I often have to minimize the template pane to enlarge the card display pane and have a better look. But when I want to return to the part of the template I'd just worked on by opening the template pane again, I find myself at the beginning of the file each time. And then I must spend some time trying to locate the code I was working on (this is where the find feature would be very useful).

[sffc]

Also would be nice to do find-and-replace.