Adding keepZeroOnFocus option

[paulodeleo]

Option for not cleaning the input on focus. Useful in combination with defaultZero + allowZero.

[sgreenfield]

+1 This should be merged!

[evindor]

+1 for the merge!

[thelinuxlich]

+1

[plentz]

looking at this right now :)

[plentz]

I'm thinking here, anybody still thinks that defaultZero is a useful option(I've never heard of somebody that uses it as false)? I'm really inclined to remove that option and always set the input to 0(formatted, of course - 0.00, for example) on focus. What do you guys think? @thelinuxlich @jpSimkins @evindor @sgreenfield @paulodeleo @bobeagan @pbalduino