move placeholder code into combobox.js only

[ericanaughton]

In order to prevent confusion for other contributors, As a contributor to LMHT, I want to move the 'input' code from script.js into combobox.js, so that code will target only the combobox, rather than the javacript in the whole site.

Acceptance Criteria:

• Line 8 in script.js needs to be moved to combobox.js
• That line of code may need to be rewritten to fit in combobox.js correctly
• The placeholder 'Search/Buscar' should be displayed when an element is not selected and when the search tool has been cleared

Given a contributor to LMHT, When I look at the code in combobox.js, I will see that the 'input' code is properly placed there, And 'Search/Buscar' is displayed when an element is not chosen.

[ericanaughton]

note: line 11 in combobox.js was followed by this comment...

     // clear the default selected option so that we see the placeholder text
    //  this.input.value = '';
    //  console.log(this.input)

[ericanaughton]

PR adorableio/LMHT#27 ready for review

[ericanaughton]

merged to adorable master