[#1723, #1725, #1726, #1727, #1729] Fixed various dialog accessibility issues.

[tonyanziano]

#1723, #1725, #1726, #1727, #1729

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Fixed the following issues within dialogs:

• the open bot dialog will no longer appear to lose focus after tabbing away from the "Browse" button
• pressing "Escape" while using the autocomplete control in the open bot dialog will no longer close the dialog
• there is now a focus indicator surrounding the close button on all dialogs
• pressing "Escape" after opening the native file browse dialog using the "Browse" button will no longer close the dialog
• fixed color contrast ratio for links within dialogs

Close icon focus indicator:

"Learn more" link color contrast:

[corinagum]

Noice!

[coveralls]

Coverage increased (+0.01%) to 65.586% when pulling 47c1db5 on toanzian/acc-dialog into 1b9a3ad on master.